The effect of levamisole on cell-mediated immunity and suppressor cell function

The immunopotentiating drug, levamisole, was found to augment human lymphocyte responses to allogeneic cells and plant mitogens in vitro. The effect was critically dose dependent and, at high doses, suppression rather than augmentation of the immune response was observed. Our hypothesis that augmentation of immune responses by the drug is due to the selective impairment of immunoregulatory suppressor activity was tested in a model using human splenic and thymic suppressor cells. Contrary to expectation, the drug was found to be capable of augmenting suppressor activity rather than abolishing it. It is concluded that levamisole is a nonspecific stimulator of lymphocyte function, irrespective of the role played by these cells in the human response.