The bovine autologous mixed leukocyte reaction: a proliferative response of non-T cells under the control of monocytes.

The culture of bovine monocyte-depleted peripheral blood mononuclear cells (PBM) (responder) with irradiated autologous undepleted PBM (stimulator) resulted in a strong proliferative response, which was called the bovine autologous mixed leukocyte reaction (MLR). A comparative study was made between this autologous MLR and the bovine allogenic MLR, with respect to the inductive requirements and the nature of responding and stimulator cells. In both the autologous and allogenic MLR, the monocyte was responsible for inducing proliferation: low concentrations of purified monocytes (greater than 95% pure) induced strong proliferative responses, while monocyte-depleted PBM (less than 0.2% monocytes) were unable to induce proliferation. Both MLRs were blocked by monoclonal antibodies specific for class II antigens of the major histocompatibility complex. The magnitude of the autologous MLR was regulated by monocytes: unirradiated monocytes induced or suppressed autologous proliferative responses depending on their concentration in the culture. Proliferating cells, identified by quantifying DNA with chromomycin A3, were all within the population of large cells. In the allogenic MLR, 50% of these large cells were T cells, as defined by monoclonal antibodies. In contrast, all of the proliferating cells in the autologous MLR were non-T cells.