Spontaneous reverse hemolytic plaque formation: III. Monocyte-mediated suppression of elevated plaque formation in autoimmune disease

The capacity of monocytes to suppress immunoglobulin secretion by B cells in human peripheral blood was investigated in vitro using spontaneous reverse hemolytic plaque formation in a liquid assay system. Monocyte suppression was not demonstrable in 10 healthy subjects. However, in 15 patients with immunopathic diseases, including systemic lupus erythematosus, chronic active hepatitis, and inflammatory bowel disease, removal of monocytes by plastic adherence resulted in up to 50-fold increases in the numbers of plaques formed by B lymphocytes, in most cases greatly exceeding the upper limit of normal. When the patients' lymphocyte preparations were reconstituted, either with autologous monocytes or with normal allogeneic monocytes, the increased plaque numbers were suppressed up to 10-fold; however, monocytes from patients did not reduce the numbers of spontaneous plaques formed by lymphocytes from normal subjects. In serial dilution experiments, the cells from patients with immunopathic diseases, in contrast to those from normal subjects, did not show a linear reduction in the numbers of plaques obtained with increasing dilutions of cells, suggesting that the suppressive influence of monocytes could be diluted out. The suppressive influence of monocytes appears to require a specific physical interaction between these cells and activated B lymphocytes. Our finding that the suppressive activity of monocytes on plaque-forming B cells is apparent only in immunopathic diseases wherein B cells are hyperactivated implies that this monocyte suppression is itself dependent on the activity of B cells.