The in vitro effects of endogenous opiates on natural killer cells, antigen-specific cytolytic T cells, and T-cell subsets.

In concert with the known effects of stress on immune function, we examined a possible neurohumoral connection. The endogenous opiates beta-endorphin, dynorphin, and methionine-enkephalin were assessed for their in vitro effects on human natural killer cell activity, antigen-specific cytolysis, and numbers and ratios of T cells and T-cell subsets. Preincubation with beta-endorphin, an opiate released into the circulation during various stresses, caused a 50% reduction in natural killer cell activity. All endogenous opiates significantly decreased antigen-specific cytolysis. Inhibition of cytolysis in vitro was not mediated through an alteration of T-cell subsets or inhibition of T-cell soluble factors (interleukin 2). The direct effects of these opiates on cytolytic T-cell and natural killer cell function may provide a link between stress and disease susceptibility.