Identification and Characterization of A Novel APC Modulating Type 2 Immunity against Influenza Virus Infection

Herein we describe a novel APC population in mice, designated LAPCs. LAPCs are BM-derived myeloid leukocytes, distinctive from other immune cells. As APCs, LAPCs respond to various virus infections including VACV, CBV3 and influenza A virus. Notably, influenza virus-activated LAPCs capture Ag in the lungs, and migrate into the DLN and spleen with delayed kinetics compared to DCs. In the DLN, influenza virus-activated LAPCs co-localize with T cells and selectively induce Th2 effector cell polarization by cell-cell contact-mediated modulation of GATA-3 expression. In support of a role for LAPCs in anti-influenza T2 immunity, adoptive transfer experiments revealed that influenza virus-activated LAPCs selectively augmented Th2 effector T cell responses in the DLN, increased production of anti-influenza immunoglobulin (Ig) including IgE in peripheral blood and increased levels of IL-5 and eotaxin in BAL fluid in recipient influenza infected mice. LAPC recipient mice exhibited exacerbated pulmonary pathology, with delayed viral clearance and enhanced pulmonary eosinophilia. Collectively, these results highlight the importance of LAPCs as novel immuno-modulators of T2 immunity during influenza A virus infection, which is implicated in both immunoprotection and immunopathology. Subsequently, we examined the immuno-modulatory effect of type-I IFN, specifically IFN-on the immune response against pulmonary influenza virus infection. We have provided evidence that a single dose of IFN- (1×105U) augmented DC migration but inhibited LAPC migration into the DLN. mIFN- treatment skewed the immune balance toward T1 immunity, identified as enhanced T1 effector T cell responses (Th1 and CTL) but diminished T2 effector T cell responses (Th2) in influenza virus infected mice. Finally, IFN- treated mice showed accelerated viral clearance and diminished pulmonary eosinophilia in lung tissue compared to control mice. Taken together, these results suggest that anti-influenza T1 and T2 immunity may be modulated differently by DCs and LAPCs, respectively. Furthermore, these results support the therapeutic potential of type I IFNs, especially IFN-, as an alternative antiviral to control both viral replication and immunopathology induced by influenza A virus infection in humans.Ph