Alteration of lymphocyte reactivities by thyroid hormones

The effects of thyroid hormones (L-T4, L-T3 and rT3) on the proliferative response of rabbit peripheral blood lymphocytes to T-cell mitogens, PHA and Con A, and B cell specific goat anti-rabbit light chain antibodies (Anti-L) were investigated. It was observed that L-T4 potentiated the lymphocyte response to mitogens and Anti-L in a dose-dependent manner: 10(-9) M and 10(-8) M had no effect while 10(-7)-10(-5) M significantly enhanced the lymphocyte response. L-T3 (10(-11)-10(-8) M) had no effect on the lymphocyte response to PHA and Con A. At 10(-7) M, L-T3 inhibited the response to PHA but not Con A. L-T3 (10(-11)-10(-7) M) suppressed the lymphocyte response to Anti-L. The suppression was directly proportional to the L-T3 concentration. rT3 (10(-11)-10(-7) M) inhibited the proliferative response to PHA and Anti-L in a dose-related manner. Its effect on the lymphocyte response to Con A was stimulatory at 10(-11) M but inhibitory at higher concentrations (10(-8) and 10(-7) M). rT3 suppressed the enhancement by L-T4 of the lymphocyte response to the mitogens and Anti-L. The degree of suppression was proportional to its concentration. This data indicated that thyroid hormones can alter the reactivities of lymphocytes. The direction and magnitude of the alteration appear to depend on the concentration of a specific thyroid hormone encountered by the responding cells.