The suppression of rejection of Nippostrongylus brasiliensis in Lewis strain rats treated with ovine prolactin. The site of the immunological defect.

Castrated male rats were treated parenterally with ovine prolactin during a primary infection with Nippostrongylus brasiliensis. Survival of the worms in the small intestine was prolonged, which suggested that prolactin inhibited rejection of the parasite. As previous studies have shown that the mechanism of rejection of helminths is at least diphasic, comprising an immuno-specific component (antibody and lymphocytes) and an immunologically non-specific component (probably involving myeloid cells and biogenic amines), it was conceptually possible that prolactin-mediated suppression of worm expulsion was due to failure in either or both components. The site of immunological impairment in prolactin-treated animals was investigated by the technique of syngeneic lymphocyte transfer. The functional activity of immune mesenteric lymph node cells, as assessed by their capacity to cause parasite rejection, was reduced by treatment of cell recipients with prolactin. In addition, lymphocytes from donors treated with prolactin during immunization were substantially less effective in rejecting an infection than cells from untreated donors when transferred to syngeneic recipients. These results showed that prolactin affected the immuno-specific component of the immune response. In order to exclude the possibility that prolactin could affect the immuno non-specific component of the rejection mechanism, lymphocytes from prolactin-treated immunized donors were transferred to prolactin-treated and untreated syngeneic recipients. The rejection of a challenge infection was suppressed to the same extent in both treated and untreated recipients, indicating that the main effect of prolactin is directed towards the immunologically specific lymphoid phase of the worm rejection mechanism.