Phytohaemagglutinin Responsiveness of Non‐adherent Nude Spleen Cells

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Abstract
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 [thymus-derived] cell mitogen phytohemagglutinin (PHA). The optimal dose of PHA was 50 .mu.l/ml for nude cells, a concentration that does not stimulate normal cells. In comparison, 2.5 .mu.l/ml PHA was optimal for cells of normal mice. Anti-.theta. serum plus complement treatment of non-adherent nude spleen cells reduced 3H-TdR incorporation by approximately 50%, suggesting that some responding cells carried the antigen. Direct immunofluorescence showed that non-adherent nude spleen cells contained 6-9% .theta.-positive cells. 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.