Antilymphocyte immunoglobulins stimulate peripheral blood lymphocytes to proliferate and release lymphokines.

Five different preparations of antilymphocyte immunoglobulins (ATG) and antithymocyte immunoglobulins (ALG) with good or little clinical response were compared for their hematopoietic and immunological activities. All ATG/ALG lots demonstrated complement-mediated cytotoxicity on peripheral blood mononuclear cells. They had different titers of antibody specificities against lymphocyte cell membrane antigens. Neither clinically effective nor ineffective lots demonstrated any apparent colony stimulating activity on bone marrow mononuclear cells. Purified Natural Killer cells failed to be stimulated by ATG/ALG in liquid culture. ATG/ALG demonstrated potent T-cell stimulating activity comparable to phytohemagglutinin. This stimulation was blocked by anti-IL-2 receptor monoclonal antibodies, and was inhibited dose-dependently by cyclosporin-A. Some clinically ineffective ATG/ALG lots also stimulated T cells to release lymphokines. The differences in these characteristics among ATG/ALG lots provide some clues to guide further efforts to elucidate a key mechanism of therapeutic effectiveness.