The immune system has evolved different types of immunities, each one specialized for the elimination of particular classes of pathogens. In response to intracellular microbes, CD4+ T-helper (Th) cells differentiate into Thl cells, which produce IFNy; in contrast, helminths induce the differentiation of Th2 cells, whose cytokines (principally IL-4, IL-5 & ILl0) induce IgE and eosinophil-mediated destruction of the pathogens. While cytokines produced early in the response are crucial in determining the Th polarization of the immune response, the mechanism by which a given pathogen stimulates a particular type of immunity is unknown. Several observations hint at a possible mechanism. First, distinct types of dendritic cell (DC) subsets differentially can induce Thl and Th2 responses. In mice, CD8(+ DCs elicit Thl cells, while CD8(- DCs induce Th2 cells. Second, different microbial stimuli signal through distinct pattern recognition receptors on antigen presenting cells (APC). For example, LPS from E.coli signals through the Toll-4 receptor (TLR4), while peptidoglycan from Staphylococcus aureus, and zymosan, signal through TLR2. Third, different microbial stimuli differentially activate DCs to elicit distinct classes of immune responses. For example, while E.coli LPS stimulates IL- 12(p70) production by DCs and primes a Thl response, P.gingivalis LPS or schistosome egg antigens (SEA) do not elicit IL-12(p70), and favor Th2 responses. In this context, it is unclear whether signaling through distinct TLRs can elicit different immune responses. Although P.gingivalis LPS, a putative TLR2 ligand, stimulates Th2 responses, it is not clear whether this is a characteristic of all TLR2 ligands, or whether this is a unique feature of P.gingivalis LPS. Furthermore, the molecular mechanism behind it is a mystery. Here, we hypothesize signaling via different TLRs can evoke qualitatively different types of responses in DCs, which ultimately mediate distinct classes of immune responses. Furthermore, we postulate that the diverse functional responses in DCs occur via activation of distinct signaling pathways. In these experiments, we will use a variety of highly purified TLR-dependant and TLR-independent microbial stimuli. Such stimuli will include the well characterized TLR4 stimulus, E.coli LPS, several different TLR2 stimuli [such as peptidoglycan (PGN), zymosan, the lipopetide STF from M.tubercolosis, and the small synthetic molecules Pam3 Cys, and MALP], the TLR5 stimulus flagellin, the TLR7 stimuli imidazoquinolines, the TLR9 stimulus CpG DNA, and the TLR3 stimulus poly-I-C, as well as classic Th2 inducers such as SEA and filarial proteins. These issues will be addressed with the following aims: ? ? Aim 1: To determine the type of antigen-specific CD4+ and CD8+ T cell responses against a soluble antigen co-injected with various TLR-dependant and TLR-independent microbial stimuli ? ? Aim 2: To determine the effects of various TLR-dependant and TLR-independent stimuli on DC phenotype, function, and survival ? ? Aim 3: To determine the intracellular signaling mechanisms by which different TLR agonists condition DCs differently to elicit distinct immune responses. ? ?
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