Reconstitution of in vitro humoral immune function in bone marrow transplant recipients.

The process by which humoral immune function is re-established following bone marrow transplantation was investigated in 50 transplant recipients. The recovery of in vitro-specific antibody production directed at sheep red blood cells was found to proceed through three phases. B cell function and helper T cell function were undetectable in the first phase (encompassing the first 5 months after transplantation), in which only suppressor cells reached functional maturity. Suppressor cells controlled responsiveness in the second phase (encompassing the period 5 to 15 months postgrafting). During this period, B cells and helper T cells became fully responsive; their activity became measurable, however, only after removal of Sephadex G-10-adherent suppressor cells. Normal responsiveness (associated with the loss of excessive suppressor cell activity) was characteristic of the third phase (over 15 months posttransplantation). Particular attention was paid to the role of suppressor cells in the recovery of humoral immune function. Their activity was positively correlated with graft-versus-host disease (GVHD), particularly of the chronic type. Suppressor cell activity in the early posttransplant period was predominantly mediated by OKT8-positive T lymphocytes, whereas suppressor cell activity in chronic GVHD patients was predominantly mediated by peripheral blood mononuclear cells that were retained on Sephadex G-10 columns, but did not express OKT8 antigen.