Ir-associated murine alloantigens: demonstration of multiple Ia specificities in H-2 alloantisera after selective absorptions.

Quantitative absorptions of anti-H-2 alloantisera with increasing concentrations of T cell-derived tumor cells of donor H-2 type has been found to remove antibodies to H-2K region antigens selectivelymsimilar results were obtained after absorptions with thymocytes of the donor strainl In each case residual antibodies reacting with Ir-associated B cell alloantigens (Ia antigens) were unmasked by this procedure. Antisera which initially contained comparable titers of Ia and H-2 activity were depleted of H-2 activity at absorbing cell concentrations which did not appreciably alter the Ia reactivities, indicating that Ia antigens, if expressed on these T cell populations, must have been present at very low concentrations relative to H-2D and H-2K region antigens. Further absorptions with spleen cells from cross-reactive strains demonstrated a multiplicity of shared and unique Ia specificites in these sera. The multiple Ia antigens detected appeared all to be codominantly expressed on the same subpopulation of lymphoid cells.