Amazon drought raises research doubts

Nature 466,423(2010); doi:10.1038/466423a

Studies highlight uncertainties over effects of climate change.

A once in a century drought struck much of the Amazon rainforest in 2005, reducing rainfall by 60 to 75% in some areas and giving scientists a window on to a future coloured by climate change.

The drought foreshadowed the Amazon drying that many climate modellers expect to see in a warmer world. But five years on, a spate of research, including 13 papers published on 20 July in a special issue of the journal New Phytologist shows that researchers are still grappling with the impact of drought and what it could reveal about the fate of the world’s largest tropical forest, a major carbon storehouse.

The debate began with a 2007 study that used data gathered by NASA’s Terra satellite to argue that the canopy of the Amazon rainforest grew and greened up during the drought suggesting that the rainforest could be resilient to dryness, at least for short periods. The phenomenon can be attributed to fewer clouds and more sunlight. But in March, a study using the same satellite data added confusion to the issue when it failed to find excessive greening.

These uncertainties are exposing the limits of space based sensors that were designed 20 years ago, says Gregory Asner, an experet in remote sensing at the Carnegie Institution's Global Ecology programme at Stanford University in California. “It’s nobody’s fault these guys are trying to squeeze blood from a stone,” says Asner, co author of a review of Amazon drought research in the New Phytologist issue. “These issues are not going to be resolved by technology that is in orbit today.”

The debate over the greening fuelled accusations that the Intergovernmental Panel on Climate Change had exaggerated when it suggested in its 2007 report that 40% of the Amazon region is highly vulnerable to drought.But longer term studies on the ground, although limited in range, have consistently showed that the forest is sensitive to drying. A 2009 analysis of ground plots found decreased growth and increased tree death from the 2005 drought and one of the New Phytologist papers documents similar results from the longest running Amazon drought experiment. After siphoning off half of the rain that fell across 1 hectare plot, researchers observed a 30% reduction in tree growth and a doubling in tree death over the course of 7 years.

But there might have been more to 2005 than just drought,according to separate report published online last month. Using a combination of satellite images and ground based tree counts, the report estimated that an unusual cluster of powerful thunderstorms in January of that year knocked down more than half a billion trees. Those results do not necessarily undercut the drought research, which took place on plots unaffected by the storms. Nonetheless, it is a reminder that “there are many factors at play”, say Carlos Nobre, a scientist at Brazil’s National Institute for Space Research in Sao Jose Dos Campos, who was not involved in the study. “Any time you try to explain basin wide phenomena with only one factor, you are probably going to be wrong,” he says.

The uncertainties in understanding drought in the  Amazon won’t be reduced without better senors in space, says Asner. In particular, he is pushing for NASA to prioritize a mission called the Hyperspectral Infrared Image –HyspIRI, which would measure the subtle color and chemcial changes in the rainforest canopy in much more detail than the Terra satellite. Despite being high on the priority list of the Earth Science community, HyspIRI is not scheduled for launch until 2020. Asner laments,” We are going to be cruising for another decade with myopic goggles on.”

Although drought has often been the focus of researchers gauging the impact of global warming on the Amazon, recent models suggest that the largest uncertainties stem from a different factor: how the forest responds to rising atmospheric carbon dioxide. By easing the burden of CO2 uptake, high concentrations of the gas reduce water loss during photosynthesis. A strong CO2 fertilization effect not only boosts growth and carbon uptake, but could also offset reduction in precipitation thus increasing resilience to drought, says Peter Cox of the University of Exeter, UK, a co author on four modelling studies in the New phytologist issue.

But in the Northern Hemisphere, fertilization experiments which involve pumping tonnes of CO2 into forest plots indicates that the effect is limited by the availability of nutrients such as nitrogen. Tropical scientists want to know if the same is true in the Amazon. “CO2 fertilization is absolutely critical in the tropics and we known absolutely nothing about it because we haven’t done the experiments,” says Cox.

Ecology: A world without mosquitoes

Nature 466, 432-434, doi:10.1038/466432a

Eradicating any organism would have serious consequences for ecosystems- wouldn’t it? Not when it comes to mosquitoes,finds Janet Frang.

Every day, Jittawandee Murphy unlocaks a hot, padloacked room at the Walter Reed Army Institute of Research in Silver Spring, Maryland to a swarm of malaria carrying mosquitoes Anopheles stephensi. She gives million of larvae a diet of ground up fish food, and offers the gravid females blood to suck from the bellies of unconscious mice they drain 24 of the rodents a month. Murphy has been studying mosquitoes for 20 years, working on ways to limit the spread of the parasites they carry. Still, she says she would rather they were wiped off the Earth.

That sentiments is widely shared. Malaria infects some 247 million people worldwide each year, and kills nearly one million. Mosquitoes cause a huge further medical and financial burden by spreading yellow fever, dengue fever, Japaneses encephalitis, Rift Valley fever, Chikunjunya virus and West Nile virus. the there’s the pest factor: they form swarms thick enough to asphyxiate caribous in Alaska and now, as their numbers reach a seasonal peack, their probosises are plunged into human flesh across the Northern Hemisphere.

So what would happen if there were none? Would anyone or anything miss them? This question is asked to scientists who explore aspects of mosquito biology and ecology and unearthed some surprising answers.

There are 3,500 named species of mosquito of which only a couple of hundred bite or bother humans. They live on almost every continent and habitat, and serve important functions in numerous ecosystems. “Mosquitoes have been on Earth for more than 100 million years,” says Murphy, “ and they have co-evolved with so many species along the way.” Wiping out a species of mosquitoes could leave a predator without prey, or a  plant without pollinator. And exploring a world without mosquitoes is more than an exercise in imagination: intense efforts are under way to develop methods that might rid the world of the most pernicious, disease carrying species.

Yet in many cases, scientists acknowledge that the ecological scar left by a missing mosquito would heal quickly as the niche was filled by other organisms. Life would continue as before or even better. When it comes to the major disease vectors, “it’s difficult to see what the downside would be to removal, except for collateral damage,” says insect ecologist Steven Juliano, of Illinois State University in Normal. A world without mosquitoes would be “more secure for us”, says medical entomologist Carlos Brisola Marcondes from the Federal University of Santa Catarina in Brazil. “The elimination of Anopheles would be very significant for mankind.”

Arctic Pests:Elimination of mosquitoes might make the biggest ecological difference in the Arctic tundra, home to mosquito species including Aedes impiger and Aedes nigripes. Eggs laid by the insects hatch the next year after snow melts, and development to adults takes only 3-4 weeks. From northern Canada to Russia, there is a brief period in which they are extraordinarily abundant, in some areas forming thick clouds. “That’s an exceptionally rare situation worldwide,” says entomologist Daniel Strickman, programme leader for medical and urban entomology at the US Department of Agriculture in Beltsville, Maryland. “There is no other place in the world where they are that much biomass.”

Views differ on what would happen if that biomass vanished. Bruce Harrison, an entomologist at the North Carolina Department of Environment and Natural Resources in Winston Salem estimates that the number of migratory birds that nest in the tundra could drop by more than 50% without mosquitoes to eat.Other researchers disagree. Cathy Curby, a wildlife biologist at the US Fish and Wildlife Services in Fairbands, Alaska, says that Arctic mosquitoes don’t show up in bird stomach samples in high numbers, and that midges are a more important source of food. “Wee as humans may overestimate the number of mosquitoes in the Arctic because they are selectively attracted to us,” She says.

Mosquitoes consume up to 300 milliliters of blood a day from each animal in a caribou heard, which are thought to select paths facing into the wind to escape the swarm. A small change in path can have major consequences in an Arctic valley through which thousands of caribou migrate, trampling the ground, eating lichens, transporting nutrients, feeding wolves and generally altering the ecology. Taken all together,then, mosquitoes would be missed in the Arctic but is the same true elsewhere?

food on the wing:”Mosquitoes are delectable things to eat and they’re easy to catch,” says aquatic entomologist Richard Merritt, at Michigan State University in East Lansing. In the absence of their larvae, hundreds of species of fish would have to change their diet to survive. “This may sound simple, but traits such as feeding behaviour are deeply imprinted, genetically, in those fish,” says Harrison. The mosquito fish Gambusia affinis for example is a specialized predator so effective at killing mosquitoes that it is stocked in rice fields and swimming pools as pest control that could go extinct. And the loss of these or other fish could have major effects up and down the food chain.

Many species of insect, spider, salamander, lizard and frog would also lose a primary food source. In one study published last month, researchers tracked insect eating house martins at a park in Camargue,France, after the area was sprayed with a microbial mosquito control agent. They found that the birds produced on average two chicks per nest after spraying, compared with three for birds at control sites.

Most mosquito eating birds would probably switch to other insects that, post mosquitoes, might emerge in large numbers to take their place. Other insectivores might not miss them at all: bats feed mostly on moths, and less than 2% of their gut content is mosquitoes. “If you’re expending energy,” says medical entomologist Janet McAllister of the Centers for Disease Control and Prevention in Fort Collins, Colorado,” are you going to eat the

Spinal injury: Sialidase gets rats moving

Functional Glycomics (08 July 2010) | doi:10.1038/fg.2010.23
After a spinal cord contusion injury, rats recover more motor function when treated with an enzyme that removes terminal sialic acids from complex gangliosides

Axons in the central nervous system (CNS) are prevented from regenerating after injury, partly due to axon regeneration inhibitors (ARIs) that accumulate at injury sites. Binding of these molecules, which include Siglec-4 (myelin-associated glycoprotein, MAG), to complementary receptors on axons results in outgrowth arrest. In a pre-clinical study, Ronald Schnaar and colleagues show that targeting the interaction of MAG with gangliosides GD1a and GT1b might provide effective therapy for spinal injuries. They report in Proceedings of the National Academy of Sciences of the USA that treatment with recombinant Vibrio cholerae sialidase, which cleaves terminal sialic acids from complex gangliosides, significantly improved recovery in rats with spinal injury.

Targeting ARIs is a promising area of spinal injury research, and sialidase treatment is known to stimulate outgrowth of CNS axons into peripheral nerve grafts. To test whether sialidase can overcome the usual inhibitory environment for axon regeneration after spinal injury, the authors used a rat model of the most common type of spinal cord injury seen in humans. Sialidase or control was delivered immediately after injury, and continuously for two weeks, and hindlimb function was evaluated using a locomotor rating scale. Staining of spinal cord sections with highly specific monoclonal antibodies to gangliosides showed that the sialidase penetrated the spine and depleted GT1b. Correspondingly, staining of GM1, the monosialoganglioside product of V. cholerae sialidase activity, was increased. GM1 does not bind MAG.

For two weeks after injury, partial recovery of hindlimb function occurred equally in the control and sialidase-treated rats, reaching an average score of 11 on the locomotor scale. However, as restorative processes had time to develop, the scores of the two groups diverged. After 5 weeks, the sialidase-treated rats reached a score of 15.6 on average, compared with 12.6 for the controls. Functionally, this represented one half of the sialidase treated rats attaining consistent coordination and frequent toe clearance, as opposed to fewer than 10% of control rats.

Sialoglycans mediate inflammation, which causes secondary tissue damage that exacerbates the initial trauma. Sialidase treatment however did not reduce lesion size or protect white or gray matter, showing that recovery is improved without any reduction in damage. Instead, the density of serotonergic axons caudal to the injury site was increased in sialidase-treated animals, consistent with the conclusion that the treatment enhances regeneration, sparing or sprouting of axons.

The sialidase used in this study is easily produced and purified, and has good stability. Improved locomotion after sialidase treatment is consistent with the conversion of MAG-binding gangliosides to GM1, but it does not exclude the possibility that other sialic acid linkages could be involved as the enzyme has broad specificity. Either way, this study shows that delivering sialidase to contused spinal cord is feasible, and might be of significant therapeutic benefit.

Related articles

von Elstermann, M. (2009) Tissue development: Cleaving an acidic sugar promotes differentiation

von Elstermann, M. (2007) Neuronal injury: Putting the brake on axonal outgrowth

Author:Emma Leah

Original research paper

1. Mountney, A. et al. Sialidase enhances recovery from spinal cord contusion injury. Proc. Natl Acad. Sci. USA(published online 7 June 2010) doi:10.1073/pnas.1006683107 | Article

Arthritis: Lubricin and inflammatory sugar

Functional Glycomics (08 July 2010) | doi:10.1038/fg.2010.24
Glycan structures of lubricin, a lubricating component of synovial fluid, are different in rheumatoid arthritis and osteoarthritis, with implications for inflammatory processes.


Osteoarthritis (OA) and rheumatoid arthritis (RA) cause debilitating joint pain, and degeneration of cartilage can be detected in both diseases by the deposition of proteoglycan fragments into synovial fluid. However, their etiologies and disease manifestations differ significantly; RA is an autoimmune disease characterized by inflammation of the synovium, whereas OA lacks an inflammatory component and is a consequence of age-related wear. Niclas Karlsson and colleagues investigated the acidic glycoprotein and proteoglycan fraction from synovial fluid samples from OA and RA patients, and unexpectedly identified lubricin (proteoglycan 4, PRG4) as the dominant component. Furthermore, they found that glycosylation of PRG4 is different in OA and RA.

The acidic protein fraction — isolated by anion exchange chromatography — formed less than 2% of the total protein content of the synovial fluid. Of this fraction, one major band after gel electrophoresis was stained by Alcian Blue, which detects acidic-type oligosaccharides and sulfated glycosaminoglycans. With the use of liquid chromatography coupled with tandem mass spectrometry (LC–MS2), this was identified as PRG4, a highly glycosylated boundary lubricant that covers the cartilage surface.

PRG4 was named as a proteoglycan in part due to a single consensus sequence for the attachment of chondroitin sulfate. It is known to contain mucin-type core 1 oligosaccharides, but detailed information about its glycosylation was lacking. The authors analyzed PRG4 glycans by LC–MS2 and identified at least nine different O-linked structures, including disialylated core 1 and core 2, and sulfated core 2 oligosaccharides.

In RA samples, there was a higher proportion of disialylated tetrasaccharide compared with singly sialylated tetrasaccharide on PRG4, with the reverse true of OA samples. This suggests a higher expression level of sialyltransferases in RA, which leads to a less complex type of O-linked glycosylation because the disialylated structures cannot be modified further in the Golgi. This is a common feature of cancer and inflammation, and in the case of PRG4 in RA it may be a protective response to combat disease progression: increased sialylation increases the negative charge around PRG4, increasing the repellant force and enhancing lubrication of joints. Alternatively, decreased sialylation in OA may be an exacerbating factor in the disease.

Sulfated core 2 oligosaccharides from PRG4 were detected in the OA samples, possibly reflecting the greater capacity for modification compared with the more highly sialylated RA oligosaccharides. A glycan epitope that forms part of the L-selectin ligand structure was also found on PRG4, but no fucosylated structures were detected. Leukocyte rolling along endothelial cell surfaces is regulated by fucosylation of L-selectin ligands, but it is not known whether sulfation of oligosaccharides has a role in inflammation. The non-fucosylated sulfated PRG4 oligosaccharide might be unique to inflammation of joint tissues.

Proteoglycans such as aggrecan are the focus of arthritic biomarker research and thus it was surprising that PRG4 was more abundant in synovial fluid. The authors speculate that loss of PRG4 at the cartilage surface could occur before the loss of extra cellular matrix components. The sample size of this study was small, and, as healthy synovial samples are difficult to obtain, there was no control available for comparison. However, this research could lead to novel biomarkers for RA, and will help to understand the enigmatic cause of synovial inflammation.

Author:Emma Leah

Original research paper

1. Estrella, R. P., Whitelock, J. M., Packer, N. H. and Karlsson, N. G.The glycosylation of human synovial lubricin: implications for its role in inflammation. Biochem. J. (published online 5 May 2010) doi:10.1042/bj20100360 | Article

A polysaccharide from the human commensal Bacteroides fragilis protects against CNS demyelinating disease

Mucosal Immunology , (9 June 2010) | doi:10.1038/mi.2010.29
J Ochoa-Repáraz, D W Mielcarz, Y Wang, S Begum-Haque, S Dasgupta, D L Kasper and L H Kasper


The intestinal microbiome may have a critical roll in susceptibility or resistance to immune-mediated diseases. Alterations of the gut microflora after oral antibiotic treatment can regulate encephalomyelitis (EAE), an animal model for human multiple sclerosis (MS). We now show that a zwitterionic capsular polysaccharide A (PSA) of Bacteroides fragilis can protect against central nervous system demyelinating disease. Oral administration with purified PSA protected mice against EAE prophylactic and therapeutically. PSA treatment enhanced CD103 expressing dendritic cells (DCs) that accumulated in the cervical lymph nodes. Exposure of naïve DCs to PSA induced the conversion of naïve CD4⁺ T cells into interleukin (IL)-10-producing FoxP3⁺Treg cells. Protection against EAE was completely abrogated in IL-10-deficient mice. Our results show an important role for a molecule from human commensal bacteria in protecting against EAE and suggest the possibility for protection in MS.

Do Parasites Make You Dumber?

What can you do to make your kids smarter? Keeping them healthy might help. A new study suggests that worldwide differences in intelligence can be explained by disparities in infectious disease. The researchers found that countries most heavily affected by infectious diseases generally had the lowest average IQs. They propose that these illnesses hinder children's brain development, though their conclusion is gathering mixed reviews.

The new research relies on data first published in 2002 in a controversial book called IQ and the Wealth of Nations. In the book, psychologist Richard Lynn of the University of Ulster in the United Kingdom and political scientist Tatu Vanhanen of the University of Tampere in Finland searched the published literature to come up with measures of average IQ for 81 countries. They also estimated IQ for another 104 countries by averaging the IQs of nearby nations. Hong Kong topped the list, with an average IQ of 107. The authors argued that national differences in IQ at least partly explained differences in national wealth. In 2006, they expanded the data to include IQ measurements from 113 countries and new estimates for 79 more.

Several groups have attempted to explain the pattern. In the new study, Christopher Eppig, a Ph.D. candidate in biology at the University of New Mexico, Albuquerque, and his colleagues propose that low IQ is tied to the toll of infectious diseases. Their idea, which the researchers call the "parasite-stress hypothesis," is that children who contract "parasites," which they define to include everything from intestinal worms to bacteria and viruses, devote more energy to fighting off infection. As a result, they have less energy available for brain development. Countries where infectious diseases are prevalent, Eppig and colleagues argue, will have lower intelligence.

To test this idea, the researchers statistically analyzed the relationship between Lynn and Vanhanen's 2006 data and 2004 data on infectious disease burden from the World Health Organization, which measures potential years of healthy life lost to premature death and illness as a result of 28 infectious diseases, including malaria, hepatitis, and tetanus. The researchers also reexamined factors that other research groups had linked to IQ, such as nutrition, literacy, education, gross domestic product, and temperature.

The numbers seem to support the hypothesis, the team will report online tomorrow in the Proceedings of the Royal Society B. When the researchers analyzed each factor independently, they found that infectious disease burden was more closely correlated to average IQ than the other variables. "Parasites alone account for 67% of the worldwide variation in intelligence," Eppig says. To further assess the relationship, the researchers built a statistical model that allowed them to test the predictive power of infectious disease burden against other variables previously associated with IQ, such as education, temperature, distance from sub-Saharan Africa, and wealth. Infectious disease burden again came out on top, although temperature and distance from sub-Saharan Africa explained some of the variation as well.

Eppig points out that their study can't rule out any of the other factors. "I would never say that parasites are the only thing affecting the global diversity of intelligence."

Maureen Black, a pediatric psychologist at the University of Maryland School of Medicine in Baltimore, is skeptical. She argues that health by itself isn't enough for full brain development. "For children to develop intellectual skills, they need not only strong bodies and the absence of infections, they also need opportunities to explore and opportunities for enrichment." Those opportunities might be lacking in countries with low average IQ.

But Richard Guerrant, a physician and infectious disease expert at the University of Virginia School of Medicine in Charlottesville, says the researchers are on the right track. His work suggests a link between diarrheal diseases, malnutrition, stunted growth, and lower IQs. The next challenge, he says, will be to uncover the exact mechanisms.

Partial and Ineffective Activation of V9V2 T Cells by Mycobacterium tuberculosis-Infected Dendritic Cells

The Journal of Immunology, 2010, doi:10.4049/jimmunol.1000966


Serena Meraviglia, Nadia Caccamo, Alfredo Salerno, Guido Sireci, and Francesco Dieli
Dipartimento di Biopatologia e Biotecnologie Mediche e Forensi, Università di Palermo, Palermo, Italy
Dr. Francesco Dieli, Dipartimento di Biopatologia e Biotecnologie Mediche e Forensi, Università di Palermo, Corso Tukory 211, 90134 Palermo, Italy. E-mail address: dieli@unipa.it

 T cells and dendritic cells (DCs) participate in early phases of immune response against Mycobacterium tuberculosis. We investigated whether a close functional relationship exists between these two cell populations using an in vitro coculture in a human system. V9V2 T cells induce full maturation of M. tuberculosis-infected immature DCs, as demonstrated by upregulation of the costimulatory CD80, CD86, CD40, and HLA-DR molecules on infected DCs after 24 h of coculture. Reciprocally, infected DCs induced substantial activation of V9V2 T cells upon coculture, which was cell-to-cell contact and TCR dependent, as demonstrated in transwell experiments. However, infected DCs selectively induced proliferative, but not cytokine or cytolytic, responses of V9V2 T cells, and this was associated with the expansion of phenotypically immature, central memory-type V9V2 T cells. Importantly, expansion of central memory V9V2 T cells and reduction of the pool of V9V2 T cells with immediate effector functions (effector memory and terminally differentiated cells) were also detected in vivo in the peripheral blood of patients with active tuberculosis, which reversed after antimycobacterial therapy. M. tuberculosis-infected DCs produced many different cytokines, but not IL-15, and addition of IL-15 to cocultures of infected DCs and V9V2 T cells caused efficient differentiation of these latter with generation of effector memory and terminally differentiated cells, which were capable of reducing the viability of intracellular M. tuberculosis. Overall, this study provides a further piece of information on the complex relationship between important players of innate immunity during mycobacterial infection.

Caseation of human tuberculosis granulomas correlates with elevated host lipid metabolism

Mi-Jeong Kim 1, Helen C. Wainwright 2, Michael Locketz 2, Linda-Gail Bekker 3, Gabriele B. Walther 4 a, Corneli Dittrich 2, Annalie Visser 2, Wei Wang 5, Fong-Fu Hsu 6, Ursula Wiehart 1b, Liana Tsenova 7 b, Gilla Kaplan 7, David G. Russell 1 *

1Department of Microbiology and Immunology, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA2Division of Anatomical Pathology, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa3Department of Medicine, The Desmond Tutu HIV Centre, Institute of Infectious Disease and Molecular Medicine, University of Cape Town, Cape Town, South Africa4Chris Barnard Division of Cardio-Thoracic Surgery, Groote Schuur Hospital, University of Cape Town, Cape Town, South Africa5Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA6Department of Internal Medicine, Washington University School of Medicine, St. Louis, MO, USA7Laboratory of Mycobacterial Immunity and Pathogenesis, Public Health Research Institute Center at UMDNJ, Newark, NJ, USA

email: David G. Russell (dgr8@cornell.edu) The progression of human tuberculosis (TB) to active disease and transmission involves the development of a caseous granuloma that cavitates and releases infectious Mycobacterium tuberculosis bacilli. In the current study, we exploited genome-wide microarray analysis to determine that genes for lipid sequestration and metabolism were highly expressed in caseous TB granulomas. Immunohistological analysis of these granulomas confirmed the disproportionate abundance of the proteins involved in lipid metabolism in cells surrounding the caseum; namely, adipophilin, acyl-CoA synthetase long-chain family member 1 and saposin C. Biochemical analysis of the lipid species within the caseum identified cholesterol, cholesteryl esters, triacylglycerols and lactosylceramide, which implicated low-density lipoprotein-derived lipids as the most likely source.  M. tuberculosis infection in vitro induced lipid droplet formation in murine and human macrophages. Furthermore, the M. tuberculosis cell wall lipid, trehalose dimycolate, induced a strong granulomatous response in mice, which was accompanied by foam cell formation. These results provide molecular and biochemical evidence that the development of the human TB granuloma to caseation correlates with pathogen-mediated dysregulation of host lipid metabolism.  EMBO Molecular Medicine Received: 16 January 2010; Revised: 3 May 2010; Accepted: 28 May 2010 10.1002/emmm.201000079

Human Innate Mycobacterium tuberculosis– Reactive abTCRþ Thymocytes

PLoS Pathog 4(2):

e39. doi:10.1371/journal.ppat.0040039

Marielle C. Gold1*, Heather D. Ehlinger2, Matthew S. Cook2, Susan K. Smyk-Pearson2, Paul T. Wille3,Ross M. Ungerleider4, Deborah A. Lewinsohn2,3, David M. Lewinsohn1,3
1 Department of Pulmonary and Critical Care Medicine, Portland VA Medical Center, Oregon Health and Science University, Portland, Oregon, United States of America,
2 Department of Pediatrics, Oregon Health and Science University, Portland, Oregon, United States of America, 3 Department of Molecular Microbiology and Immunology,
Oregon Health and Science University, Portland, Oregon, United States of America, 4 Doernbecher Cardiothoracic Surgery, Doernbecher Children’s Hospital, Portland,
Oregon, United States of America.



The control of Mycobacterium tuberculosis (Mtb) infection is heavily dependent on the adaptive Th1 cellular immune response. Paradoxically, optimal priming of the Th1 response requires activation of priming dendritic cells with Th1 cytokine IFN-c. At present, the innate cellular mechanisms required for the generation of an optimal Th1 T cell response remain poorly characterized. We hypothesized that innate Mtb-reactive T cells provide an early source of IFNc to fully activate Mtb-exposed dendritic cells. Here, we report the identification of a novel population of Mtb-reactive CD4 abTCRþ innate thymocytes. These cells are present at high frequencies, respond to Mtb-infected cells by producing IFN-c directly ex vivo, and display characteristics of effector memory T cells. This novel innate population of Mtb-reactive T cells will drive further investigation into the role of these cells in the containment of Mtb following infectious exposure. Furthermore, this is the first demonstration of a human innate pathogen-specific abTCRþ T cell and
is likely to inspire further investigation into innate T cells recognizing other important human pathogens.

An isoleucine-zipper motif enhances costimulation of human soluble trimeric GITR ligand

Cellular & Molecular Immunology 7, 316-322 (July 2010) | doi:10.1038/cmi.2010.7


Glucocorticoid-induced tumor-necrosis factor receptor (GITR) and its ligand, GITRL, play significant roles in regulating immune responses. It is clear that human soluble GITRL (hsGITRL) transduces signal activity through multiple oligomerization states. To develop human soluble trimeric GITRL protein as a potential therapeutic target, we explored the link of the isoleucine-zipper (ILZ) motif to the N-terminus of the human soluble GITRL with two leucine sequences. hsGITRL, with the ILZ motif (ILZ-hsGITRL), was firstly expressed in Escherichia coli, which exhibited a predominant trimer when identified by Sephadex G-100 filtration and non-reducing SDS–polyacrylamide gel electrophoresis (SDS-PAGE). The significantly higher biological activity of the ILZ-hsGITRL compared with hsGITRL was confirmed by CD4⁺ T proliferation, interferon-γ (IFN-γ) secretion and binding activity assay. To reveal and compare the underlying mechanisms, the level of extracellular signal-regulated kinase-1/2 (ERK1/2) phosphorylation was examined, indicating that ILZ-hsGITRL induced more persistent and stronger ERK1/2 activation than hsGITRL. In conclusion, the incorporation of an ILZ motif could markedly improve the costimulation of hsGITRL.

Mycobacterium tuberculosis promotes HIV trans-infection and suppresses MHC-II antigen processing by dendritic cells

J. Virol. doi:10.1128/JVI.02303-09


Morgan A. Reuter, Nicole D. Pecora, Clifford V. Harding,David H. Canaday, and David McDonald^*

Department of Molecular Biology and Microbiology, Department of Pathology, Division of Infectious Diseases, Case/UH Center for AIDS Research, Case Western Reserve University School of Medicine; Geriatric Research, Education and Clinical Center, Louis Stokes VAMC, Cleveland, OH 44106

M. tuberculosis (Mtb) is a leading killer of HIV infected individuals worldwide, particularly in sub-Saharan Africa, where it is responsible for up to 50% of HIV-related deaths. Infection by HIV predisposes individuals to Mtb infection, and co-infection accelerates the progression of both diseases. In contrast to most other opportunistic infections associated with HIV, increased risk of Mtb infection occurs during early stage HIV disease, long before CD4 T cell counts fall below critical levels. 

We hypothesized that Mtb infection contributes to HIV pathogenesis by interfering with dendritic cell (DC) mediated immune control. 

DCs carry pathogens like Mtb and HIV from sites of infection into lymphoid tissues,where they process and present antigenic peptides to CD4 T cells. Paradoxically, DCs can also deliver infectious HIV to T cells without first becoming infected, a process known as trans-infection.

 LPS-activated DCs sequester HIV in pocket-like membrane invaginations that remain open to the cell surface, and individual virions are delivered from the pocket into T cells at the site of contact during trans-infection. Here we report that Mtb exposure increases HIVtrans-infection and induces viral sequestration within surface-accessible compartments identical to those seen in LPS-stimulated DCs. 

At the same time, Mtb dramatically decreases the degradative processing and MHC-II presentation of HIV antigens to CD4+ T cells. Our data suggests that Mtb infection promotes a shift in the dynamic balance between antigen processing and intact virion presentation, favoring DC-mediated amplification of HIV infections.

Tumor Necrosis Factor-α Blocker Induced Tuberculosis

J Rheumatol 2010;37:7; doi:10.3899/jrheum.100058



Patients who are treated with anti-tumor necrosis factor-α (anti-TNF-α) blockers are at risk of reactivation of latent tuberculosis (TB) infection (LTBI). The study by Dr. Malaviya, et al describes an approach to the diagnosis of LTBI prior to anti-TNF-α therapy1. 
Screening tests they advise are tuberculin skin test (TST), interferon-γ release assay, or Quantiferon TB
Gold (QTB Gold), chest radiograph (CXR), and computed tomogram (CT) of the thorax. We describe 2 patients who developed active TB while taking infliximab, despite the recommended screening tests being negative.
Case 1: In March 2009, A 30-year-old male, with long standing ankylosing spondylitis (AS), complained of worsening of axial symptoms in spite of adequate nonsteroidal antiinflammatory drugs (NSAID). As the AS
was active, infliximab therapy was offered. Baseline laboratory findings were: hemoglobin: 9.5 g/dl, leukocyte count: 10,012 cells/mm3, erythrocyte sedimentation rate (ESR) 45 mm/h, platelets: 416,000/mm3, serum
glutamic pyruvic transaminase 22 IU/l, and serum creatinine 0.8 mg/dl. The LTBI screen tests including CXR, TST, and QTB Gold test were negative. CT thorax was not done. He was given 2 doses of infliximab (3
mg/kg per dose) 5 months apart. Three weeks after the second dose he developed a low grade fever and cough. There were scattered crackles on auscultation and the CXR showed consolidation in the right upper and middle zones. Although three sputum acid-fast bacilli (AFB) smears and AFB culture were negative, anti-TB therapy (ATT) was started on clinical grounds. The patient showed clinical and radiological resolution in 6
weeks’ time.
Case 2: In March 2008, a 13-year-old boy was diagnosed to have Juvenile AS with peripheral arthritis. He improved with NSAID over 4 weeks. Six months later the AS relapsed and was refractory to NSAID and
methotrexate. Laboratory reports were: hemoglobin: 10.7 g/dl, leukocyte count: 10,700 cells/cm3, platelets: 430,000 cells/cm3, ESR: 100 mm/h, and CXR: normal; TST and QTB Gold were both negative. Infliximab (3 mg/kg) was given June 5. In September 2009, he developed low grade fever, loss of appetite, and dry cough of 2 week duration. CXR showed right sided pleural effusion, aspiration of which revealed a lymphocytic predominant exudate with elevated adenosine deaminase level (156 iu), consistent with TB pleural effusion. ATT was initiated and he is now improving.


It is important to recognize and treat LTBI prior to institution of anti-TNF-α therapy. In both our patients, an attempt was made to exclude LTBI using the screen recommended by Malaviya, et al. As both patients
initially showed no clinical evidence of TB, with a negative CXR, TST, and TB gold tests, a CT of the chest was not done. Despite having a negative screen, both our patients developed active TB after initiation of infliximab therapy.
False negative TST as a result of immune suppression can result in a false negative screen for LTBI. 
Park, et al showed that, of 86 patients who received anti-TNF-α therapy with a negative TST at the baseline2, TST (repeated annually) converted to positive after a median interval of 33.3 months in 32.6% of patients. Interferon-γ release assay (IGRA) testing was found to have a 68.6% concordance with TST. Hence, combined testing with TST and IGRA can to an extent overcome the false negative TST.


We recently reported that by T cell specific ELISPOT (T spot) assay, the prevalence of LTBI in healthy, urban Indians is around 80%. Unlike the TST, this is a specific assay for Mycobacterium tuberculosis, not confounded by previous bacillus Calmette Guerin BCG vaccination, or infection with environmental mycobacteria. The T-spot TB assay also has a lower likelihood of being rendered false negative by prednisolone therapy versus TST. This test could help identify LTBI in patients who are TST and IGRA negative.
In endemic regions like India, a new TB infection may be misclassified as a TB flare. Further, ELISPOT test, the TST and TB gold test, fail to differentiate between latent and active TB. This distinction is crucial, in order
to choose between initiation of anti-TB prophylaxis or that of full-fledged ATT4. Since a normal chest radiograph does not rule out LTBI or active TB, correlation of IGRA and TST with clinical likelihood of LTBI is important . This is especially true in India, where a CT chest cannot always be done due to cost constraints.
In conclusion, not even a battery of tests can completely exclude LTBI. Hence, even with a negative screen, the possibility of TB flare, or development of new TB infection, must always be kept in mind while initiating
anti-TNF therapy. In such patients, combination of TST and IGRA, with regular repetition of these tests, will increase the likelihood of diagnosis of LTBI. It is also recommended that LTBI prophylaxis be continued in those patients receiving anti-TNF-α therapy who have been treated for TB disease prior to initiation of the same.


PRIYANKA KHARBANDA, MD; RUCHA DAGAONKAR,
CANCHI BALAKRISHNAN, MD; ZARIR F. UDWADIA, MD, FRCP;
Rheumatology and Pulmonology Units, PD Hinduja Hospital, Mumbai,
India.


REFERENCES
1. Malaviya AN, Kapoor S, Garg S, Rawat R, Shankar S, Nagpal S, et
al. Preventing TB flare in patients with inflammatory Rheumatic
diseases receiving Tumor Necrosis Factor alpha (TNF alpha)
inhibitors in India — an audit report. J Rheumatol
2009;36:1414-20.
2. Chung SJ, Kim JK, Park MC, Park YB, Lee SK. Positive
conversion of tuberculin skin test and performance of interferon
release assay to detect hidden tuberculosis infection during
anti-tumor necrosis factor agent trial. J Rheumatol
2009;36:2416-20.
3. Lalvani A, Nagvenkar P, Udwadia Z, Pathan AA, Wilkinson KA,
Shastri JS, et al. Enumeration of T cells specific for RD1- encoded
antigens suggests a high prevalence of latent mycobacterium
tuberculosis infection in healthy urban Indians. J Infect Dis
2001;183:469–77.
4. Winthrop KL, Chiller T. Preventing and treating
biologic-associated opportunistic infections. Nat Rev Rheumatol
2009;5:405-10.
5. Martin J, Walsh C, Gibbs A, McDonnell T, Fearon U, Keane J, et
al. Comparison of interferon {gamma} release assays and
conventional screening tests before tumour necrosis factor {alpha}
blockade in patients with inflammatory arthritis. Ann Rheum Dis
2010;69:181-5.