In experimental sepsis, C5ar1- or NK cell-deficient mice showed increased survival associated with decreased TNF-alpha and IFN-gamma production. The decreased cytokine production results from C5aR-mediated regulation of DC and NK cell functions, suggesting that C5a faciliates the deleterious immune responses in sepsis by modulating NK/DC cross-talk. Further, C5a is critical for the development of appropriate CD4+ T cell responses in L.major and T.gondii infection as well as CD8+ T cell responses in influenza or LCMV infection. However, the molecular mechanisms underlying C5aR-mediated regulation of NK cell receptor functions in infection and its impact for the induction of antigen-specific CD4+ and CD8+ T cell responses remain elusive. Data from Fusakio et al. suggest that C5a regulates the expression of NKp46. Using N-Ethyl-N-nitrosourea (ENU), two germline mutants, designated Ace and Chip, have been identified in the Hoebe lab. Coarse mapping and next generation sequencing revealed the Chip phenotype to result from a missense mutation in the Immunoreceptor tyrosine-based switch motif (ITSM) domain of the signaling lymphocyte activation molecule (SLAM)-related receptor 2B4 (CD244) that can elicit both activating as well as inhibitory signals on NK cells. The causal variant in the Ace mutant was found to be a missense mutation in the SH2 domain of Slp76, an adapter molecule for which the function in NK cells is poorly defined. Interestingly, Ace mutants showed no abnormalities in T cell development or T cells responses. Both strains have normal NK cell development but are susceptible to T.gondii infection as a result of increased or decreased NK cell-dependent immune responses. Here, we aim at investigating the role of C5aR signalling in NK cell function and its interaction with specific NK cell receptors identified through ENU mutagenesis in experimental T. gondii infection.

Aims:

1. Define the role of C5aR signaling in DC-dependent and -independent activation of NK cells in vitro
2. Delineate the role of C5aR signaling in NK cell-mediated control of T. gondii infection
3. Define the potential cross-talk between CD244, Slp76 and C5aR signaling pathways in NK cells for the induction of T.gondii-specific CD4 and CD8 T cell responses in vitro and in vivo