Sec61 is essential for antigen cross-presentation and the development of lupus nephritis (171.4)

Abstract Objective: We repeatedly immunized mice normally not prone to autoimmune diseases with the same antigen to show that repeated immunization reproducibly led to the development of SLE, where full-matured CTL generated via antigen cross-presentation caused lupus nephritis. Here we clarify the molecular mechanism of antigen cross-presentation in relation to SLE. Methods: Bone marrow-derived dendritic cell (BMDC) from BALB/c mice was cultured with fluorescent-labeled OVA. Early endosome antigen 1 (EEA1), calnexin and Sec61 were detected using immunofluorescent staining. For in vivo study, BALB/c mice were repeatedly immunized with OVA to evoke SLE. Exotoxin A was co-immunized with OVA to inhibit Sec61. Proteinuria and IFNγ-producing CD8+ T cell were measured. Results: Upon culture of BMDC, OVA was co-localized with the endosomal marker EEA1, and subsequently separated from EEA1. OVA was never co-localized with the endoplasmic reticulum (ER) marker calnexin. Instead, OVA was co-localized with a translocon, Sec61, indicating that OVA was exported directly from endosome to cytoplasm via Sec61. Generation of both CTL and lupus nephritis was abrogated by in vivo treatment with exotoxin A, an inhibitor of Sec61. Thus, export of antigen from endosome to cytoplasm via Sec61 is essential for antigen cross-presentation. Conclusion: Direct export of antigen from endosome to cytoplasm via Sec61 is essential both for antigen cross-presentation and induction of lupus nephritis.