Immunocompetence of pinealectomized and simultaneously pinealectomized and thymectomized rats.

The cellular and antibody-mediated immune responsiveness was studied in adult rats which had the pineal and/or the thymus gland removed within 36 hours after birth. The immunolgical parameters measured were: Skin graft rejection, haemolytic plaque formation, and haemagglutinating antibody formation in response to sheep red blood cells and the stimulation of lymphoid cells from the spleen by phytohaemagglutinin in lipopolysaccharide. The removal of the pineal gland had little effect on the degree of immunocompetence in normal or immunosuppressed animals. In some of the immunological tests an accelerated response was observed, which suggests that lymphoid cells from pinealectomized or pinealectomized-thymectomized animals proliferate more rapidly upon contact with antigen or mitogen. This accelerated cell proliferation, unlike the immunodepression of the host, could explain the enhanced growth of transplantable tumors observed in pinealectomized animals.