Summary Host defense against viruses and intracellular parasites depends on effector CD8+ T cells whose optimal clonal expansion, differentiation, and memory properties require signals from CD4+ T cells. Here we addressed the role of dendritic cell (DC) subsets in initial activation of the two T cell types and their co-operation. Surprisingly, initial priming of CD4+ and CD8+ T cells was spatially segregated within the lymph node and occurred on different DC with temporally distinct patterns of antigen-presentation via MHCI vs. MHCII molecules. DC that co-present antigen via both MHC molecules were detected at a later stage; these XCR1+-DC are the critical platform involved in CD4+ T cell augmentation of CD8+ T cell responses. These findings delineate the complex choreography of cellular interactions underlying effective cell-mediated anti-viral responses, with implications for basic DC subset biology as well as for translational application to the development of vaccines that evoke optimal T cell immunity.

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BackgroundIn rural sub-Saharan Africa, endemic populations are often infected concurrently with several intestinal and intravascular helminth and protozoan parasites. A specific, balanced and, to an extent, protective immunity will develop over time in response to repeated parasite encounters, with immune responses initially being poorly adapted and non-protective. The cellular production of pro-inflammatory and regulatory cytokines and chemokines in response to helminth, protozoan antigens and ubiquitous allergens were studied in neonates, children, adults and the elderly.ResultsIn children schistosomiasis prevailed (33%) while hookworm and Entamoeba histolytica/E. dispar was found in up to half of adults and the elderly. Mansonella perstans filariasis was only present in adults (24%) and the elderly (25%). Two or more parasite infections were diagnosed in 41% of children, while such polyparasitism was present in 34% and 38% of adults and the elderly. Cytokine and chemokine production was distinctively inducible by parasite antigens; pro-inflammatory Th2-type cytokine IL-19 was activated by Entamoeba and Ascaris antigens, being low in neonates and children while IL-19 production enhanced “stepwise” in adults and elderly. In contrast, highest production of MIP-1delta/CCL15 was present in neonates and children and inducible by Entamoeba-specific antigens only. Adults and the elderly had enhanced regulatory IL-27 cytokine responses, with Th2-type chemokines (MCP-4/CCL13, Eotaxin-2/CCL24) and cytokines (IL-33) being notably inducible by helminth- and Entamoeba-specific antigens and fungus-derived allergens. The lower cellular responsiveness in neonates and children highlighted the development of a parasite-specific cellular response profile in response to repeated episodes of exposure and re-infection.ConclusionsFollowing repeated exposure to parasites, and as a consequence of host inability to prevent or eliminate intestinal helminth or protozoa infections, a repertoire of immune responses will evolve with lessened pro-inflammatory and pronounced regulatory cytokines and chemokines; this is required for partial parasite control as well as for preventing inadequate and excessive host tissue and organ damage.

21 ] i may in turn activate TRPA 1 leading to a greater rise in [Ca 21 ] i . We also recognize that these studies were performed in vitro, which may not fully recapitulate what occurs in vivo. Finally, studies using primary bronchial epithelial cells from deceased donors are intrinsically limited by the availability of donor cells, especially in the pediatric age group. Additionally, history of atopic status and lung function is frequently not available, as well as comorbidities and cause of death. Thus, it is possible that the age effect could be explained by other factors and future studies will need to be done using cells from identified samples from patients with documented asthma status and severity.In conclusion, the results of this study show for the first time that lower airway epithelium from asthmatic children displays elevated basal TRPV 1 activity when compared with that of nonasthmatic controls. We have also shown that RSV infection of epithelial cells from asthmatic children-but not from adults-leads to an increase in overall TRPV 1 activation. Pharmacological inhibition of TRPV 1 may lead in the future to strategies that might reduce the impact of RSV infections in both asthmatic and nonasthmatic children.