Suppressor lymphocyte activity in normal and immunodeficient horses.

Equine lymphocytes incubated with Con A and isolated on discontinuous BSA density gradients suppressed mixed lymphocyte reactions in a cell dose- and Con A dose-dependent manner. Suppressor lymphocytes were radiosensitive, even after the initial Con A incubation phase was completed. Suppressor activity was consistently demonstrated using peripheral blood mononuclear leukocytes from normal horses, but was absent in thymus cells and variably present in lymph node cells. Suppressor lymphocytes were present in horses with selective IgM deficiency, and within neoplastic lymph nodes from a horse with lymphosarcoma and concomitant IgM deficiency. Suppressor cells were not detected in 5 of 6 horses with severe combined immunodeficiency.