The effect of hypophysectomy on the immune response.

Twenty-one-day-old rats were hypophysectomized or sham-operated and challenged with sheep red blood cells 5 or 21 days after operation. Although the sizes of the bodies and lymphoid organs were greatly decreased in the hypophysectomized animals no significant difference was found in the numbers of plaque forming cells or serum antibody titres against the sheep red blood cells. The hypophysectomized rats showed a cell depletion in the perifollicular zone of the spleen follicles, but no obvious histological changes in the thymus. It is concluded that pituitary hormones are not directly necessary for the formation of humoral antibodies.