Monocyte-reactive antibodies in patients with systemic lupus erythematosus.

Cold-reactive antibodies cytotoxic for peripheral monocytes from more than half of normal donors were found in the sera of 2 of 25 patients with systemic lupus erythematosus (SLE) and 1 of 26 with rheumatoid arthritis (RA), and they were absent in 25 normal sera. In contrast, lymphocytotoxic activity for T or B lymphocytes was found in over half of the lupus sera. The antibodies to monocytes were primarily IgM and exhibited varying specificities. Some of the antibodies were directed against antigenic determinants common to monocytes, T and B cells, or against determinants shared between monocytes and one lymphocyte type. One serum possessed a high titer of antibodies that were specific for monocytes. The clinical significance of antimonocyte antibodies remains to be established.