Ontogeny of antigen-presenting activity of haptenized cells in mice: early development of syngeneic T cell-stimulatory cells in thymus.

Trinitrophenyl (TNP)-modified thymus cells stimulated the proliferation of syngeneic spleen T cells in in-vitro culture supplemented with syngeneic normal mouse serum. The stimulatory activity of the TNP-adult thymus cells was about a half of that of TNP-adult spleen cells. Neither thymus cells depleted of adherent cells before haptenization nor TNP-thymus cells treated with anti-Ia antiserum served as stimulators. TNP-thymus cells, but not TNP-spleen cells, prepared from cells of newborn mice within one week after birth were almost as competent as adult TNP-thymus cells. TNP-spleen cells first became effective when spleen cells were obtained from mice at the age of 3 weeks. Ineffectiveness of the newborn spleen cells is not due to immunosuppressive function. These results indicate that Ia-bearing antigen-presenting cells appear earlier in the thymus than in the spleen. The intrathymic Ia+ adherent cells, however, seem not to be autonomously potent for accessory cell function, since haptenized thymus cells were not able to stimulate T cells if adherent cells were removed from the responder cells. This suggests that the second type of adherent cells residing in spleen but not in thymus is required for the activation of T cells in response to TNP-thymic adherent cells.