Blastogenic factor: its role in the mixed leukocyte culture reaction

The MLC‐CML reaction depends on cooperation between different subsets of T lymphocytes in which soluble mediators may play a critical role. Evidence is presented that cell‐free supernatants from mixed cultures, containing blastogenic factor (BF) activity can, together with solubilized membrane preparations, induce a primary cell‐mediated lympholysis (CML) reaction of the same order of magnitude as intact allogeneic stimulating cells. Furthermore, BF alone can induce secondary mixed leukocyte culture (MLC) and CML reactions very efficiently. The results described suggest that BF is produced in response to activation by LD determinants, probably by helper T cells, and that the target of BF is the cytotoxic lymphocyte. It would appear that regulation of CML activity may be mediated by BF, and exhaustion of the mediator may be responsible for the decline of cell proliferation and effector function in the MLC reaction.