Dendritic cell presentation of antigens from apoptotic cells in a proinflammatory context: Role of opsonizing anti-β2-glycoprotein I antibodies

Objective. To verify whether opsonization of apoptotic cells skews the outcome of apoptotic cell antigen presentation by dendritic cells (DCs). Methods. RMA cells, which were engineered with a mutant ovalbumin (OVA) protein and were devoid of the leader secretory sequence (OVA-RMA), underwent ultraviolet irradiation to induce apoptosis. Binding of anti-β₂- glycoprotein I antibodies (anti-β₂GPI) and phagocytosis of apoptotic cells were assessed by flow cytometry and confocal microscopy. Presentation of processing antigens and major histocompatibility complex (MHC) class II- restricted or MHC class I-restricted antigens was assessed using OVA-specific T cell hybridomas. Results. Anti-β₂GPI facilitated presentation of epitopes from internalized apoptotic cells to MHC class II-restricted, but not to class I-restricted, T lymphocytes. DCs challenged with supernatants of apoptotic cells did not activate OVA-specific T cells, making it unlikely that anti-β₂GPI complexed with antigen released from dying cells plays a role in antigen presentation. DCs challenged with low numbers of anti- β₂GPI-opsonized apoptotic cells secreted interleukin-1β (IL-1β), tumor necrosis factor α, and IL-10 in an autocrine/paracrine manner. Conclusion. Opsonization influences the outcome of the disposal of low numbers of apoptotic cells by DCs. This implies that soluble factors bound to apoptotic cells modulate their immunogenicity.