Reduced susceptibility to anti-Fab antibodies of B cells in patients with systemic lupus erythematosus.

We have observed the effects of rabbit F(ab')2 anti-Fab antibodies (a-Fab Ab) on the differentiation of B cells in normal subjects and in patients with systemic lupus erythematosus (SLE). Peripheral blood lymphocytes were obtained and cultured with or without the addition of a-Fab Ab, and IgG- and IgM-secreting cells were assayed by reverse hemolytic plaque assay after 7 days of culture. In normal subjects, the spontaneous development of IgG- and IgM-secreting cells in the cultures of lymphocytes without pokeweed mitogen (PWM) was markedly suppressed by a-Fab Ab. In patients with SLE, however, the spontaneous development of IgG- and IgM-secreting cells was almost unchanged in the presence of a-Fab Ab. The effects of a-Fab Ab on immunoglobulin production induced by PWM were different in active and inactive SLE. The inhibitory effect of a-Fab Ab on PWM-induced development of IgG- and IgM-secreting cells was observed in normal subjects and inactive SLE patients. In active SLE patients, however, the production of IgG and IgM was not significantly increased by PWM and almost unchanged with the addition of a-Fab Ab. These findings show that B cells in SLE are much less susceptible to a-Fab Ab than normal B cells.