Monocyte (macrophage)-specific antibodies in patients with systemic lupus erythematosus (SLE)

Antibodies reactive for monocytes (macrophages) were found in the sera of patients with systemic lupus erythematosus (SLE). These antibodies were present in both IgG and IgM fractions and worked under both warm (37 degrees C) and cold (4 degrees C) conditions. These antibodies were specific for monocytes, because cytotoxic antibodies for monocytes were absorbed with monocytes, but not with T cells, B cells, and granulocytes. Furthermore, their specificity is also different from anti-HLA-DR antibody. The presence of these antibodies correlated with the activity of disease. They were found in 12 of 14 active SLE and 7 of 16 inactive SLE patients. The treatment of normal monocytes with these SLE sera and complement resulted in the depletion of their accessory function for T-cell activation and their phagocytic activity. In the previous paper, we reported that the accessory function of monocytes for T-cell activation was impaired in SLE patients. These results suggest that monocyte-specific antibodies play an important role in the pathogenesis of SLE through disturbing the monocyte regulatory function for immune responses.