Phytohaemagglutinin responsiveness of non-adherent nude spleen cells.

Non-adherent spleen cells from athymic nude mice showed incorporation of tritiated thymidine (3H-TdR) at a level comparable to that of non-adherent cells of normal mice when stimulated with the T-cell mitogen phytohaemagglutinin (PHA). The optimal dose of PHA was 50 microliter/ml for nude cells, a concentration that does not stimulate normal cells. In comparison, 2.5 microliter/ml PHA was optimal for cells of normal mice. Anti-theta serum plus complement treatment of the non-adherent nude spleen cells reduced 3H-TdR incorporation by approximately 50%, suggesting that some of the responding cells carried the theta antigen. Direct immunofluorescence showed that the non-adherent nude spleen cells contained 6-9% theta-positive cells. In comparison, more than 80% of the PHA-induced nude blast cells were theta-positive. PHA-induced DNA synthesis of normal mouse spleen cells was inhibited by adherent nude spleen cells. No theta-antigen or surface immunoglobulin could be demonstrated on these inhibitory cells, suggesting that they belong to the macrophage system of the nude mouse spleen.