Specific suppression of the in vitro parent anti-hybrid reaction. I. Characterization of a suppressor cell induced in hybrids by pretreatment with parent-strain spleen cells

Spleen cells from B6D2F1 hybrid mice pretreated with 5 X 10(7) B6 spleen cells iv 7 days earlier (B6-pretreated B6D2F1) exhibit a reduced capacity to stimulate the in vitro proliferative and anti-D2 CTL responses of B6 spleen cells. This inability of B6-pretreated B6D2F1 spleen cells to stimulate B6 spleen cells efficiently is due neither to the absence of stimulating cells bearing the D2 alloantigens nor to the destruction of B6 responding cells, but to the presence in the B6-pretreated B6D2F1 cell population of a suppressor mechanism, since the addition of B6-pretreated B6D2F1 spleen cells to a culture of normal B6 responding and irradiated B6D2F1-stimulating spleen cells can suppress the B6 anti-B6D2F1 response. This suppression is mediated by a nylon adherent, Thy-1-negative cell of parent-strain origin which is radioresistant at 2000 R. This suppressor cell is not induced by the injection to B6D2F1 hybrids of spleen cells from the other parent strain (D2) or an allogeneic strain (C3H). It does not suppress either the response of the other parent (D2) or an allogeneic strain (C3H) to B6D2F1 antigens, or the response of B6 cells to an allogeneic strain (C3H).