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MITOGEN‐STIMULATED LYMPHOCYTE INHIBITION BY SUPERNATANTS OF CROWDED LYMPHOCYTOBLASTS

SUMMARY An inhibitor of blastogenesis has been found in supernatants of cultured lymphocytoblasts grown under crowded conditions. It was produced maximally at a concentration of 1 × 107 cells/cm2. This inhibitor suppresses the in vitro response of normal human peripheral blood lymphocytes to the mitogens phytohemagglutinin, pokeweed, and concanavalin A, as well as allogeneic cells. By itself it is neither stimulating nor cytotoxic. The inhibitor has been characterized by size on gel chromatography and its clution pattern places it in a molecular weight range of 40,000–70,000. The material is eluted on ion-exchange chromatography in a conductivity range of 14,000–18,000 μmhos. The inhibitor is stable at 56 C for 30 min and labile at 80 C for 30 min. Treatment at pH 2.4 caused complete loss of activity, while the other pH levels had less or no effect.