Hiroshi Nakabayashi

Lymphocyte calmodulin and its participation in the stimulation of T lymphocytes by mitogenic lectins

Summary— Calmodulin was purified from human tonsillar lymphocytes utilizing calcium‐dependent binding of calmodulin to fluphenazine‐Sepharose. The molecular weight and phosphodiesterase activation of the lymphocyte calmodulin were very similar to those of purified bovine brain calmodulin. Trifluoperazine (TFP), a calmodulin inhibitor, suppressed lymphocyte stimulation as assessed by 3H‐thymidine incorporation into DNA of lectin‐stimulated lymphocytes. TFP had no effect on the early 45Ca2+ uptake induced by mitogenic lectins, although this latter was inhibited by verapamil which also suppressed the 3H‐thymidine incorporation. The results are in keeping with the interpretation that the inhibition of T cell stimulation by TFP was not due to suppression of Ca2+ uptake, but due to inactivation of Ca2+‐calmodulin complex which might be formed subsequent to Ca2+ entry into the cell.

Mechanisms of Interleukin-2-Mediated Signaling and role of Calcium in T cell Mitogenesis

In T lymphocytes stimulated by concanavalin A (Con A), interleukin 2 (IL-2) acts on the late G1 stage of the cell cycle. Ca2+ uptake by T cells was not enhanced with the stimulation of Con A (initiation) or IL-2 (late G1 stage), but Ca2+ requirement was observed at the two stages. These results indicate that the enhancement of Ca2+ uptake is not necessary, but intracellular Ca2+ may act as an important messenger in T cell mitogenesis.

Seasonal variation in mitogenic response and subsets of human tonsillar lymphocytes

Abstract A seasonal variation was observed in the mitogenic response of human tonsillar lymphocytes and in the percentages of each subset. We found that the responsiveness of lymphocytes to mitogens was high in summer and low in winter. The identification of lymphocyte subsets by using monoclonal antibodies indicated that the percentages of T4 positive cells and T8 positive cells increased in summer and decreased in winter. The most significant change was observed in the percentages of T8 positive cells. The significant relationship between the mitogenesis and the percentages of T8 positive cells was observed. These results indicated that the seasonal variation in lymphocyte mitogenesis might depend on the size of T8 positive cells.