LONG-TERM EFFECTS OF THYROID-HORMONE ON LYMPHOCYTE SUBSETS IN SPLEENSAND THYMUSES OF MICE

We examined the effects of the long-term administration to mice of thy roid hormone or propylthiouracil (PTU) on lymphocyte subsets in spleen s, and thymuses to clarify whether hyperthyroxinemia itself causes the changes in lymphocyte subsets, such as the marked increase in CD5(+) B cells and decrease in natural killer (NK) cells, observed in hyperth yroid Graves' disease. Both the number and proportion of splenic NK (T hy-1(+) asialo GM1(+)) cells were increased in hyperthyroxinemic mice treated with thyroxine (T-4) for both short and long terms (8 and 32 w eeks, respectively), those of splenic and thymic T (CD5(+) sIgM(-)) ce lls were increased only in hyperthyroxinemic mice treated for 32 weeks , and those of splenic B (sIgM(+)) cells and CD5(-) B cells were incre ased only in hypothyroxinemic mice treated with PTU for 32 weeks, comp ared with those in euthyroid mice. These data indicate that 1) long-te rm hyperthyroxinemia increases splenic and thymic T cells and splenic NK cells, but not CD5(+) B cells, in mice, 2) long-term hypothyroxinem ia induced by PTU treatment increases splenic B cells and CD5(-) B cel ls, and 3) hyperthyroxinemia itself does not cause the changes in CD5( +) B cells and NK cells, which are observed in hyperthyroid Graves' di sease, in mice.