Influence of the thymus on the capacity of female mice to reject male skin grafts

The ability of female mice to reject H-Y-incompatible, but otherwise histocompatible, male skin grafts differs greatly from strain to strain, as is illustrated particularly by the C57BL strain (B6 and other sublines), termed "H-Y rejector," because females invariably and promptly reject C57BL male skin, in comparison with the C3H strain, termed "H-Y nonrejector," because females characteristically accept male C3H skin. To assess the extent to which the thymus governs this rejector vs. nonrejector status, two studies were made. In the first, lethally irradiated B6 (C57BL) and C3H females were restored with (B6 X C3H)F1 female cells, providing a graft-vs.-host-free milieu for differentiation of the same immunopoietic cell population in B6 vs. C3H hosts. With respect to (B6 X C3H)F1 male skin grafts, B6 hosts responded as rejectors and C3H hosts as nonrejectors, signifying that rejector vs. nonrejector status was determined by the host during immunopoiesis. That the main organ responsible for rejector vs. nonrejector determination is the thymus was shown in a second study. Previously thymectomized (B6 X C3H)F1 females received a histocompatible graft of thymus from either B6 or C3H neonatal females and were restored with donor-marked (B6-Ly-5a X C3H)F1 female cells after lethal irradiation. With respect to (B6 X C3H)F1 male skin grafts, the recipients of B6 thymus grafts responded generally as rejectors and the recipients of C3H thymus grafts responded uniformly as nonrejectors.