Enhancement of the immune response in vitro by arsenic.

We examined the effect of arsenic (As) on the immune response of mice to sheep erythrocytes, assaying the spleen for plaque-forming cells (PFC). The effect of As on the PFC response to sheep erythrocytes was dose-dependent. At high doses of As the PFC response was erythrocytes was dose-dependent. At high doses of As the PFC response was suppressed, whereas it enhanced the response at low doses. The suppression was due to the cytotoxic action of As against lymphocytes generally. On the other hand, enhancement was seen on the addition of As at the start of the culture or as a result of pretreatment of normal spleen cells with As. Even low doses of As were cytotoxic, to both B and T cells. They differed, however, in their susceptibility to As. When normal spleen cells were added to the culture of As-treated spleen cells, the enhancement of the PFC response was reversed. Suppressor-inducer B cells, in the normal spleen cells, could not induce suppressor T cells from As-treated spleen cells. And As did not affect suppressor T cells. These findings indicate that As deletes the precursors of suppressor T cells from normal spleen cells, and thus enhances the immune response.