MLR blast cells generated in mutant-standard strain combinations bind H-2K and H-2D antigens.

Strains CBA (M523) (= M523) and CBA differ by a mutation which has been mapped genetically into the K region of the H-2 complex. Similarly, strains B 10.D2 (M504 (= M504) and b 10.D2 differ in a mutation which occurred in the D region. The data presented in this study show that mixed lymphocyte culture in M523 anti-CBA and M504 anti-B 10.D2 strain combinations leads to the release of membrane fragments from the stimulating cells and binding of these fragments by blast cells. The fragments always carry H-2K (in the M523 anti-CBA combination) or H-2D (in the M504 anti-B 10.D2 combination) antigens present in the stimulating and absent in the responding cells (antigens H-2.60 and H-2.40, respectively). Although Ia antigens may occasionally be present on the CBA membrane fragments, these antigens do not participate in the M523 anti-CBA MLR stimulation. The data thus demonstrate that serologically detectable H-2K and H-2D antigens can induce a MLR and that a mutation can change properties of H-2K or H-2D molecules so that the alteration is detectable by both serological means and lymphocyte activation assays.