FcgR-activated neutrophil regulation of T cells in nephritis and vasculitis - ABSTRACT Systemic lupus erythematosus (SLE) is a heterogeneous disease characterized by IgG-antibody-antigen immune complexes (ICs). About 50% of patients develop lupus nephritis, up to 36% develop vasculitis that can lead to life-threatening cardiac inflammation, and the presence of lupus nephritis increases the incidence of cardiovascular events. Immune cell abnormalities underly these processes but the mechanisms driving them are poorly understood. Both activated neutrophils and self-reactive T cells activated by antigen presenting cells (APCs) play roles in disease pathogenesis. Conventional dendritic cells, cDC1s are recognized as the professional APCs for their unique ability to activate naïve T cells and cross-present extracellular antigens to CD8 T cells. We detected neutrophils with markers of APCs, termed nAPC, in patients with lupus nephritis and the frequency of nAPCs clinically correlated with disease activity. Accordingly, we show that the interaction of ICs with FcγRs on neutrophils generates highly immunogenic APCs (nAPCs). In FcγR humanized mice expressing the human FcγRIIIB only on neutrophils, an anti-FcγRIII mAb conjugated to a model T cell antigen, Ovalbumin (αRIII-Ova) (replicating the effects of FcγRIIIB’s natural ligands, i.e. small ICs), robustly expands naïve Ova-specific CD4 and CD8 T cells compared to IgG-Ova control, even in the genetic absence of cDC1s. In the context of nephrotoxic nephritis (NTN), a model of crescentic glomerulonephritis mimicking the effector phase of lupus nephritis, αRIII-Ova further expands Ova-specific T cells compared to IgG-Ova that migrate to the nephritic kidney and accumulate in the renal draining LNs (dLN). We will test the hypothesis that circulating ICs containing self-antigens in SLE generate nAPCs that initiate the activation of self-reactive T cells in 2o lymphoid organs and with the assistance of nAPC activated cDC1 induce T cell trafficking to tissues and dLN that fuels systemic autoimmunity and increases the risk for secondary coronary vasculitis. Our studies will use NTN, an inducible model of coronary vasculitis, scRNA-sequencing, multiplexed spatial imaging of the spleen from NTN mice and human lupus patients with and without nephritis, and CRISPR/Cas9 based neutrophil or T cell specific deletion of genes of interest. This proposal is innovative as it suggests that IC-stimulated neutrophils play a central role in initiating and perpetuating T cell mediated dysfunction in glomerulonephritis and subsequent secondary cardiac inflammation. It is significant as it may offer new insights into disease pathogenesis, addresses a substantial unmet clinical need, and provides knowledge that can be used to develop novel targeted therapeutic interventions that disrupt neutrophil-mediated T cell dysregulation in both glomerulonephritis and secondary coronary vasculitis in lupus. Importantly, the function of nAPCs can’t be assumed by more conventional APC as nAPCs are immunogenic in the absence of adjuvant and FcγRs play a major role in neutrophil’s acquiring potent APC function.
