Inhibition of in vitro lymphocyte proliferation by serum from acquired immune deficiency syndrome patients depends on the ratio of cells to serum in culture.

The effect of serum from patients with acquired immune deficiency syndrome (AIDS) on cultures of normal human peripheral blood mononuclear cells stimulated with phytohemagglutinin (PHA) has been studied. It has been found that AIDS sera are inhibitory when compared with control sera from healthy individuals. The inhibitory activity in the AIDS patients' sera is dilutable with normal serum, is dependent on the number of cells present in culture and the amount of serum added, and cannot be attributed to a deficiency of nutrients in these sera. Inhibition of proliferation occurs even when AIDS serum is added to cultures of normal cells several hours after stimulation with PHA. In one patient who was being treated with plasmapheresis, decreases in serum inhibitory activity were found after pheresis procedures and were coincident with increases in the number of circulating T4-positive lymphocytes.