B cell stimulating activity of metallothionein in vitro

The effect of metallothionein (MT) on lymphocytes was studied in vitro. Rabbit MT induced the proliferative responses of mouse splenocytes at concentrations of 1–25 μg/ml. MT synergistically enhanced Con A- or LPS-induced proliferative response of splenocytes. A similar effect was also observed for rabbit splenocytes at a similar concentration. Free heavy metals such as Cd and Zn only weakly stimulated splenocytes. 2-mercaptoethanol (2-Me) abrogated the effect of MT, suggesting that thiols in MT play an important role for splenocyte response. MT stimulated splenocytes from MT-knockout mice as well as those from normal control mouse. The responder cells for MT stimulation were B cells and MT also induced B cell differentiation to produce Ig. MT induced the calcium influx of B cells, but not T cells. These results indicate that MT has a potent immunomodulating activity, especially on B cells.