Effect of triiodothyronine on the short-lived and concanavalin-A generated suppressor T-cell functions

Evidence concerning the role of hyperthyroidism per se in suppressor cell dysfunction in Graves' disease is conflicting. To investigate this issue, we studied the effect of triiodothyronine (T3) administration to ten healthy volunteers for 7 days on spontaneous (short-lived) and Concanavalin A (Con A)-induced suppressor cell activities. The short-lived suppressor cell index is a ratio of [3H] thymidine incorporation induced by Concanavalin A in lymphocytes preincubated for 24 h (to remove adherent cells) to that of non-incubated lymphocytes; the more active the adherent suppressor cells, the higher this index. The mean short-lived suppressor cell index rose from a mean of 2.46 +/- 0.15 (+/- S.D.) before T3 treatment to 3.29 +/- 0.46 (p less than 0.01) after 7 days of T3. Concanavalin A-induced suppressor cell activity, which measures the potential suppressive activity of lymphocytes triggered by Con A is expressed as the percentage decrease in [3H] thymidine incorporation by lymphocytes cultured with Con A for 72 h in relation to that by fresh lymphocytes. Con A-induced suppressor cell activity also improved from 55.8% +/- 2.5 before T3 treatment to 62.4% +/- 1.9 (p less than 0.05) at 7 days of this treatment. These studies show that within the time limitations of the study, T3 appears to enhance short-lived and Concanavalin A-induced suppressor cell activities.