Abstract
Accumulating evidence suggests that DNA-anti-DNA antibody immune complexes are endocytosed by immune cells, where they ligate intracellular nucleic acid sensors. This results in production of type I interferon or other cytokines, which may be a significant pathogenetic mechanism in systemic lupus erythematosus (SLE). Most studies thus far have been performed using cell-lines or peripheral blood mononuclear cells, but it remains unclear whether cells from the brain can take up such immune complexes. Because permeability of the blood-brain interfaces is suggested to be increased and autoantibodies are detected in cerebrospinal fluid of SLE patients with neuropsychiatric manifestations, we hypothesize that DNA-anti-DNA immune complexes may be internalized by cells in the central nervous system and cause dysregulation of neural networks. As a first step to test this hypothesis, here we investigated whether anti-DNA antibodies can be internalized by live brain cells in vitro.
Primary culture rat astrocytes were incubated for 1 h at 37°C with or without anti-DNA monoclonal antibodies. After washing, fixation, permeabilization and blocking, internalized anti-DNA antibodies were detected by a fluorescent labeled second antibody. We observed that a dsDNA-specific monoclonal antibody entered the nucleus, while a monoclonal antibody cross-reactive with phospholipid and DNA entered the cytoplasm. Isotype-matched control IgG did not enter the cells, suggesting that they were viable and the cell membrane and nuclear membrane were intact at that time. When the cells were incubated at 4°C, internalization of the anti-DNA antibodies was almost completely abolished. This suggests that antibody internalization was not by passive transfer but is an energy-dependent process. Given that astrocytes play indispensable roles in maintaining the function of neural networks, these results may provide a novel perspective on the pathogenetic mechanisms of the neuropsychiatric manifestations often presented in SLE.