Immunomodulation in rats by transplantable anterior pituitary tumors

The effect on the immune response of the MtT/W5 (W5), MtT/W10 (W10) tumors of Wistar-Furth rats and of MtT/F4 (F4) tumor transplantable in Fischer 344 rats was examined. Antibody response to sheep red blood cells and contact sensitivity reactions to dinitrochlorobenzene (DNCB) were used as immune parameters. In intact rats the W5 tumor suppressed the antibody response as much as did hypophysectomy (Hypox). The antibody response of Hypox rats was marginally improved by this tumor. Contact sensitivity was not suppressed in intact animals and the poor reactivity of Hypox rats was reconstituted to normal levels by W5. Treatment with bromocriptine (BRC) had no influence on tumor growth or on the immune reactivity of tumor-bearing hosts. The W10 tumor suppressed antibody formation, but not contact sensitivity in intact animals; the antibody and the DNCB response of Hypox animals was reconstituted partially, by this tumor. BRC treatment of tumor-bearing animals mimicked the effect of Hypox in this system. The F4 tumor suppressed antibody formation in intact rats and did not reconstitute the reactivity of Hypox rats. The DNCB response was not influenced by this tumor in intact animals and it was partially reconstituted in Hypox rats. Again, the reactivity of BRC-treated animals was similar to that of Hypox tumor-bearing animals. These results indicate that pituitary tumors may alter the immune reactivity of their hosts significantly.