Inhibition of the mixed leukocyte reaction by alloantisera in man. II. Incidence and characteristics of MLC-inhibiting antisera from multiparous women.

The incidence of MLC-inhibiting antibodies was determined in 42 pregnancy sera. MLC's were carried out between the cells from the serum donor and her busband in the presence of nonimmune AB serum and the test serum. Fifty per cent of the sera reduced the MLC response to less than 40% of the control values. Only four sera had lymphocytotoxic activity. The inhibition was strong against the specific immunizor, less strong against random unrelated cells and weak against cells which were SD-identical with the serum donor. Absorptions with lymphocytes and platelets were carried out. Lymphocytes removed activity in three of the four sera tested. Platelets removed activity from one serum. It was concluded that both anti-LD and anti-SD anti-bodies were able to inhibit the MLR at the stimulator cell level.