IN-VITRO EFFECTS OF MELATONIN ON MITOGEN-INDUCED LYMPHOCYTE-PROLIFERATION AND CYTOKINE EXPRESSION IN YOUNG AND OLD RATS

Melatonin (MLT) treatment in vivo has been shown to have immunomodulat ory and anti-immunosenescent effects in the mouse model. In the presen t report, the in vitro effect of MLT on mitogen-induced lymphocyte pro liferation and cytokine expression was evaluated in a rat model. Splen ic lymphocytes were isolated from young (6 months) and old (24 months) F344 rats and were incubated with MLT in the presence or absence of m itogens. The proliferative response to concanavalin A (ConA) or PMA pl us ionomycin was measured in splenocytes or T cells isolated from youn g and old rats. In addition, the induction of interteukin-2 (IL-2) and interferon-gamma (IFN-gamma) production was measured in MLT-treated a nd untreated lymphocytes isolated from young and old rats. The ConA-in duced lymphocyte proliferation and IL-2 expression were significantly lower and induction of IFN-gamma production was significantly higher i n splenocytes and purified T cells isolated from old rats compared to splenocytes and T cells isolated from young rats. Treatment of lymphoc ytes with MLT did not significantly alter ConA-induced lymphocyte prol iferation or IL-2 or IFN gamma expression in lymphocytes isolated from either young or old rats. On the basis of these data, we conclude tha t in vitro MLT treatment had no immunomodulatory effect on lymphocytes from rats.