Antibody-induced internalization and degradation of PLA2R amplifies CD4+ T cell activation

Rationale: Phospholipase A2 receptor (PLA2R) is the predominant autoantigen in primary membranous nephropathy (PMN), accounting for approximately 70% of clinical cases. However, the mechanisms by which PLA2R initiates and sustains autoimmunity in PMN remain unclear. PLA2R belongs to the mannose receptor (MR) family, members of which have been shown to undergo endocytosis and lysosomal degradation for MHCII-mediated antigen presentation. This study investigates whether antibody binding promotes PLA2R internalization and lysosomal processing to enhance MHCII-mediated antigen presentation and CD4⁺ T cell activation, thereby contributing to the perpetuation of autoimmunity in PMN. Methods: Multiple PLA2R-overexpressing cell lines were generated by lentiviral-mediated overexpression of PLA2R. Imaging and western blot were employed to assess the effects of anti-PLA2R antibodies, derived from PMN patients or produced in-house, on PLA2R internalization and degradation. To define the specific endocytic pathway involved, we used pharmacological inhibitors of endocytosis as well as PLA2R constructs lacking the endocytic domain. Finally, T cell activation was evaluated using OT-II CD4⁺ T cells co-cultured with PLA2R-ovalbumin (OVA)-expressing mouse dendritic cells treated with anti-PLA2R antibodies. Results: Binding of anti-PLA2R antibodies triggers clathrin-mediated endocytosis and lysosomal trafficking of PLA2R. Antibody-induced PLA2R degradation was effectively prevented by specific endocytosis inhibitors or by deletion of the PLA2R endocytic domain. Furthermore, PLA2R-OVA-expressing mouse dendritic cells exposed to PLA2R antibodies enhanced the activation of OVA-specific CD4⁺ T cells both in vitro and in vivo. Conclusions: This study demonstrates that anti-PLA2R antibody induces internalization and lysosomal degradation of PLA2R, a process that may enhance MHC class II-mediated antigen presentation and promote the expansion of antigen-specific CD4⁺ T cells. This mechanism could establish a self-reinforcing feedback loop that perpetuates autoimmune responses in PMN.