Effect of hemic cells on hybrid resistance.

Injection of various parental strain hemic cells reduces the ability of the F1 hybrid to resist growth of grafted hemopoietic tissue from the same parent strain. Such an effect can be exerted by cells from lymph nodes, spleen, bone marrow, or thymus, the peritoneal macrophages, and the peripheral blood leukocytes. Embryonic and adult liver cells or blood erythrocytes do not inhibit hybrid resistance. It is assumed that hemic cells inhibit hybrid resistance through an effect on the hemopoietic microenvironment. The mechanism of this effect cannot be considered the result of a graft-versus-host reaction since lymphoid cells which are "immune" or "tolerant" to the hybrid antigens possess inhibitory activity similar to that of intact lymphoid cells. The hybrid resistance inhibitory cells maintain the inability of "parent-in-F1 hybrid" type chimeras to express hybrid resistance for at least 2 months.