The different chemokine profile in HIV-exposed seronegative persons

The studies on human population infected with or exposed to HIV have brought the description of several virus-refractory phenotypes. Among them are long-time non-progressors and HIV-exposed seronegative persons. The first group is able to control virus replication without the anti-retroviral therapy, maintain the normal CD4 T cell number and avoid the chronic immune activation that is normally associated with HIV infection. In consequence, long-time non-progressors can live with the presence of HIV for many years with minimal or without any ill effects. The second group is less widely known and comprises people who despite the persistent exposure to the virus do not become infected. In ordinary circumstances HIV gets into the body through mucosal surfaces at genital organs. HIV-exposed seronegative persons (HESN) appear to differ from the virus-sensitive population in terms of chemokine profile at the natural infection site.

The link: http://www.nature.com/mi/journal/v5/n3/abs/mi20127a.html

The study is conducted among Kenyan commercial sex workers divided into three categories. The experimental group includes HESN women, whereas control groups are HIV-1 negative women and HIV-1 infected patients. Authors analyze the cytokine/chemokine profile in the cervicovaginal lavage of each group. They detects that MIG and IP-10 (two IFN-γ inducible chemokines involved in the leukocyte trafficking) and cytokine IL-1α are expressed at lower level in the HESN cohort. Both chemokines are involved in the mucosal migration of activated CD4 T cells – the main HIV target. Hence one of HESN phenotype explanation might be that these people display the state of immune quiescence at their genital mucosa and simply do have enough number of activated CD4 T cells to become infected by virus.

To validate this point investigators examine plasma chemokine/cytokine profile in all studied groups as lymphocytes migrate to mucosal surfaces according to the chemokine gradient between blood and mucosa. They demonstrate that MIG levels in HESN group were higher in systemic compartments than at the genital mucosa whereas the HIV-1 negative population shows the opposite trend. Additionally, HESN subjects uniquely display the decreasing gradient for IP-10 from plasma to mucosal surfaces. The supportive data in this paper include the analysis of CXCR3 (the receptor bound by MIG and IP-10) on CD4 and CD8 T cells collected from the genital mucosa. Authors also study the expression of antiproteases in the genital tract as they are important factors regulating mucosal chemokine levels. It would be interesting to know what really drives the decreased chemokine levels in the genital tract of HESN.

J Lajoie, J Juno, A Burgener, S Rahman, K Mogk, C Wachihi, J Mwanjewe, F A Plummer, J Kimani, T B Ball, and K R Fowke (2012). A distinct cytokine and chemokine profile at the genital mucosa is associated with HIV-1 protection among HIV-exposed seronegative commercial sex workers Mucosal Immunology DOI: 10.1038/mi.2012.7

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Degradation of chemokines by food-borne bacterium

The diet, previous or ongoing encounters with infectious organisms and parasites as well as bacterial microflora that inhabit the intestinal tract or other mucosal surfaces – all these factors influence the quality of immune responses. To mention just one relevant case – in developing countries people appear to be less affected by autoimmune diseases but in wealthy societies autoimmunity represents the constantly growing problem. This phenomenon may be partially due to the much lower level of contact with parasitic worms in places where higher civilization level is attained. It has been shown that some parasites (Schistosoma mansoni is the best known example) seem to be able to exert the regulatory effect on mammalian immune responses and thereby reduce the risk of inappropriate reactions to self-antigens. The microflora may also be a factor in autoimmunity development. The publication I have found describes details of interactions between probiotic-associated bacterial molecule and pro-inflammatory chemokines many of which are involved in autoimmune diseases.

The link: http://www.cell.com/cell-host-microbe/retrieve/pii/S1931312812000662

This report is a continuation of previous study where it has been shown that a cell surface protein from Lactobacillus casei strain derived from VSL#3 (a probiotic food product used in management of ulcerative colitis) can degrade IP-10 (interferon gamma induced protein 10, known also as CXCL10 – a pleiotropic pro-inflammatory chemokine). Authors use molecular biology techniques to prove that the described earlier protein is a serine protease. The action of this protease is not specific to IP-10 as it degrades a number of other chemokines (CXCL9, CXCL11, CXCL12, CX3CL1 and CCL11). On the other hand several well-known pro-inflammatory agents like RANTES, IL-6, IFNγ and TNF are not affected.

Investigators attempt to translate L.casei-dependent chemokine degradation into the physiological setting. To this end they use TNFΔARE/+ model (mice lacking post-transcriptional regulation of TNF that develop spontaneous inflammatory bowel disease). The intraperitoneal injections of L.casei-conditioned media reduces several pro-inflammatory parameters like ileal IP-10 level, activation of certain signaling pathways and infiltration of ileum by mononuclear cells or T cells. Authors proceed to screening fecal human samples for bacteria displaying similar abilities and identify microflora-derived L.casei strain that also degrades IP-10. This strain and its mutated version with the disrupted copy of gene encoding the protease in question are used to feed mice with intestinal inflammation (the different disease model is used this time – Rag2-/- mice that received IL-10 deficient CD4 T cells). The presence of L.casei with protease reduces cecal inflammation indices like IP-10 level or T cell influx whereas the protease-deficient strain is unable to influence the above parameters.

Such capacity of L.casei – the regulation of immune responses via degradation of potent pro-inflammatory agents has provoked me to hypothesize about the origin of dairy products consumption. The hypothesis I have is a tentative one and I am not sure whether it reflects the true reason-effect relationship. I am also aware that it drifts far away from the data presented in the discussed paper and I do not know if it has not has been already proposed by somebody else. Let me state few facts: (1) L.casei belongs to the bacterial group called LAB (lactic acid bacteria). LAB comprises species that are associated with mammalian mucosal surfaces and food products including milk (they are not limited to milk, however). (2) The human capacity to consume milk and dairy products beyond infancy period dates back to the time of agricultural revolution and the transition from hunter-gatherer lifestyle. Interestingly, genomic data indicate that the enzyme metabolizing milk lactose has undergone huge selection events which are comparable to the selection that in the recent human history affected factors responsible for skin pigmentation.

What was the true reason behind our ability to digest milk as adults? Could it be the presence of food-borne bacteria that were able to regulate mucosal immune responses? The transition to the agriculture had to involve many dramatic changes in human diet (most probably in human microbiota, too) and first farmers tended to be actually less healthy than hunters-gatherers (I need to indicate that I have no specialist knowledge of ethnography and I rely here on several general science books I have read – most notably Pandora’s Seed: Why the Hunter-Gatherer Holds the Key to Our Survival by Spencer Wells). Might the extended period of milk consumption be able to alleviate the stress on human physiology imparted by modifications to the original human lifestyle?

Such line of thinking brings another question. What could be special about the original human microbiome? The remaining hunter-gatherer people are distinctively free from diseases comprising so-called metabolic syndrome (source: The Cambridge Encyclopedia of Hunters and Gatherers). Might it be partially due to specific microbiota they harbour? The only relevant report I could find indicates that the oral microbiome of Batwa pygmies is significantly more diverse than in their agricultural neighbors (High diversity of the saliva microbiome in Batwa Pygmies: PLoS One. 2011; 6(8):e23352). Maybe we can find solutions to ever-increasing burdens of civilization in those vanishing people?

von Schillde MA, Hörmannsperger G, Weiher M, Alpert CA, Hahne H, Bäuerl C, van Huynegem K, Steidler L, Hrncir T, Pérez-Martínez G, Kuster B, Haller D. (2012). Lactocepin Secreted By Lactobacillus Exerts Anti-Inflammatory Effects By Selectively Degrading Proinflammatory Chemokines Cell Host&Microbe DOI: 10.1016/j.chom.2012.02.006

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IL-21 reporter mouse shines more light on follicular helpers

Follicular helpers are the special population of CD4 T cells that localize to germinal centers and are involved in enhancing the humoral response. They are distinguishable from other CD4 T cell subsets by their joint expression of CXCR5, ICOS, PD-1 and the transcription factor Bcl-6 as well as the capacity to secrete IL-21 cytokine. The recent paper describes a novel model to study the biology of TFH – the IL-21 reporter mouse. Such mouse has a GFP encoding cassette knocked-in into IL-21 locus to create the animal that expresses simultaneously IL-21 and GFP. IL-21 is not a cytokine characteristic exclusively for TFH but in conditions applied by this study the GFP presence in secondary lymphoid organs is restricted to activated CD4 T cells that are positive for CXCR5 and PD-1 thus being follicular helpers according to the accepted definition. The ability to track TFH population in vivo allows answering questions concerning their fate after the primary immune response is over and germinal centers undergo resolution.

The link: http://www.nature.com/ni/journal/v13/n5/full/ni.2261.html

There are two main contributions that this paper adds to the existing knowledge of TFH. First, it dissects follicular helpers into IL-21 secreting and IL-21 negative populations and characterizes both subsets. Second, it analyzes the ability of TFH to form the memory compartment and participate in recall responses. In order to track IL-21 secreting cells among TFH authors follow general follicular helper population (defined as CD4+CD44+CD62LCXCR5+PD-1+cells) after the immunization with NP-KLH (a T cell-dependent antigen). They discover that GFP-positive cells constitute a stable proportion of TFH (~30-40%) at every time points during the course of primary response. Both IL-21 secreting (GFP+) and IL-21 negative (GFP) subpopulations are mostly equivalent in terms of transcription factors (Bcl-6, IRF4, Blimp-1, T-bet and GATA3 tested) and cytokine expression (IFN-γ, IL-4 and IL-10 examined), proliferation and functional abilities (NP-specific GC B cell response analyzed). The only difference between two subsets was an increase in transcripts encoding T-bet, IFN-γ and IL-10 among GFPcells.

The potential of TFH to participate in recall responses is tested by adoptive transfer approach. Follicular helpers generated in the course of immune response to influenza virus (flu infection similarly to NP-KLH immunization leads to the formation of GFP+ and GFP– subsets of TFH) were injected into congenic recipients challenged subsequently with the same virus. It is observed that antigen-experienced  TFH have the ability to expand on re-stimulation in vivo. Transferred follicular helpers are then analyzed by their surface marker expression and cytokine profile.  In secondary lymphoid organs TFH have a definite propensity to continue as TFH. However, at effector sites (lungs) the vast majority of former follicular helpers become conventional effectors CD4 T cells. Follicular helpers retain also the substantial ability to release cytokines on antigen re-exposure. It is interesting to know that TFH have some plasticity and may end up doing different tasks after germinal centers of primary immune response are disbanded.

Lüthje, K., Kallies, A., Shimohakamada, Y., Belz, G., Light, A., Tarlinton, D., & Nutt, S. (2012). The development and fate of follicular helper T cells defined by an IL-21 reporter mouse Nature Immunology, 13 (5), 491-498 DOI: 10.1038/ni.2261

Neutrophils, IL-17 and oral microbiota in periodontitis

Th17 response has the ability to induce migration of neutrophils from the bloodstream into inflamed tissues. Neutrophils form the important part of immune defense and as such are equipped with a number of anti-microbial and pro-inflammatory measures. However, as in the case of other immune effectors their action may also have the darker side – collateral injuries to the surrounding environment. Such immune-mediated bystander damages underlie the pathology of periodontitis which is the inflammatory disease afflicting gingival tissue. I have read very interesting publication that describes how the intricate interplay between neutrophils and IL-17 cytokine may regulate periodontitis development.

The link: http://www.nature.com/ni/journal/v13/n5/full/ni.2260.html

Periodontitis is a disease that inflicts neutrophil-mediated inflammatory lesions to the tooth-supportive tissue which may result in loosening and loss of teeth. Old mice just like old humans are prone to develop periodontitis. Del -1 is a negative regulator of neutrophil extravasation which is known to be expressed by endothelial cells (cells that line blood vessels). Authors initially explored Del-1 expression pattern in various age groups as the association between the age and the disposition to excessive inflammation is well known. They concluded that Del-1 level in the gingival tissue of older mice represented only a small portion (~25%) of Del-1 amount found in younger mice. They also found that the decrease in Del-1 expression correlated with more pronounced tooth bone loss and the enhanced neutrophil influx to gingiva. The Del-1/neutrophils/bone loss relationship was confirmed by using Del-1 deficient mice. Apart from that it was shown that the increase in gingival neutrophil infiltration mediated by the deletion of Del-1 could be counteracted by knocking out LFA-1 which is a positive regulator involved in neutrophil tissue migration.

Del-1 deletion seemed to augment the local Th17 response as Del-1 deficient mice expressed more IL-17A (IL-17C and IL-17F were also increased) as well as p40 and p19 (subunits of IL-23 which is strong Th17 response inducer). Remarkably, the analysis of IL-17RA-deficient mice has shown that inflammatory bone loss characteristic for periodontal injuries was completely abolished when there was no IL-17 signaling (interestingly, there was no difference between IL17RA-deficient strain and combined IL-17RA/Del-1 mutant). IL-17RA deletion also enhanced Del-1 expression in gingival tissues. Investigators confirmed the link between lack of IL-17 signaling and increase in Del-1 amount by neutralization method (injection of monoclonal anti-IL17 antibody to gingiva) and bone marrow chimeras experiments. The last approach revealed that the lack of IL-17RA on non-hematopoietic cells was important in regulating Del-1 expression. Finally, authors explored whether administration of Del-1 into inflamed gingival tissues could have the therapeutic potential

Beyond results discussed above this publication contains data on how genetic background that underlies quantitative aspects of neutrophil migration into gingiva may influence the oral microbiota. These data are somewhat counter-intuitive (as it is sometimes the case for things happening at mucosal surfaces). The leading theme of this paper is that Del-1 down-regulation or absence promotes the enhanced neutrophil infiltration and augments inflammatory-mediated tooth bone loss. However, Del-1 deletion (and hence more gingival neutrophils, which after all are thought to be cells with anti-microbial properties) actually stimulates more bacterial growth. This not just one odd result, because when Del-1 deletion is combined with LFA-1 knockout (a positive regulator of neutrophil extravasation) or IL-17RA knockout (removing thus the important part of signaling involved in the neutrophil influx) the number of oral anaerobic bacteria goes back to normal values. Thus to sum up, the excessive inflammation seems to boost but not to restrict the growth of oral microbiota. Authors do not follow this observation but I think it is very interesting phenomenon.

Eskan, M., Jotwani, R., Abe, T., Chmelar, J., Lim, J., Liang, S., Ciero, P., Krauss, J., Li, F., Rauner, M., Hofbauer, L., Choi, E., Chung, K., Hashim, A., Curtis, M., Chavakis, T., & Hajishengallis, G. (2012). The leukocyte integrin antagonist Del-1 inhibits IL-17-mediated inflammatory bone loss Nature Immunology, 13 (5), 465-473 DOI: 10.1038/ni.2260