In vitro secondary MLR. III: Hybrid histocompatibility determinants.

With cells obtained from long-term mixed lymphocyte culture (MLC) we have have demonstrated hybrid histocompatibility determinants that are recognized as mixed lymphocyte reaction (MLR)-stimulating determinants. Hybrid determinants can also be detected (1) in an in vitro assay for effector cells that measure inhibition of immunoglobulin secretion by LPS-blasts, and (2) in DTH-like responses of in vitro-primed cells injected into "B" mice and challenged in vivo with stimulator cells. The possible implications of these findings for the physiologic function of MLR determinants are discussed.