Accelerated skin graft rejection following transfer of cells sensitized to a " weak" histocompatibility antigen(s)

C3H/HeJ mice were immunized with either CBA/J or C57L/J skin grafts and then tested for secondary responses against both strains. Secondary responses were measured by six-day graft rejection, ability of syngeneic spleen cells to transfer skin-graft imnunity to sublethally irradiated mice, and graft-versus-host disease (GVHD) in lethally irradiated CBA/J mice receiving C3H/HeJ spleen cells. Although failure to transfer a primary response against " Creak" histocompatibility antigens with syngeneic spleen cells was noted, the secondary responses demonstrated a cross-reacting antigen(s) which seems to be of greater imnunologic strength than the postulated H-13 difference. Possible explanations for this finding include the existence of multiple undescribed loci with cross-reacting alleles, or an increase in immunogenicity of " weak" transplantation antigens when acting in concert with " stronger" antigens.