Journal of Experimental Medicine, Vol 147, 708-718, Copyright © 1978 by Rockefeller University Press
Induction in vivo and in vitro of terminal deoxynucleotidyl transferase by thymosin in bone marrow cells from athymic mice
NH Pazmino, JN Ihle and AL Goldstein
Terminal deoxynucleotidyl transferase (TdT) expression in bovine serum
albumin (BSA) gradient-fractionated bone marrow cells was examined in NIH
Swiss nu/nu and thymectomized C57BL/6 mice. In nude mice, TdT levels were
approximately 10% of those of thymus-bearing littermates. In C57BL/6 mice,
thymectomy caused a time-dependent loss of TdT activity in bone marrow
cells. To determine whether or not not the apparent thymic requirement for
TdT expression in bone marrow was mediated by thymic hormones, we examined
the effects of thymosin fraction 5. Treatment of either NIH Swiss nu/nu or
thymectomized C57BL/6 mice with thymosin fraction 5 restored the levels of
TdT activity in BSA gradient-fractionated bone marrow cells to normal.
Moreover, treatment of BSA gradient-fractionated bone marrow cells from NIH
Swiss nu/nu or thymectomized C57BL/6 mice in tissue culture with thymosin
fraction 5 induced TdT expression. In tissue culture, TdT induction was
optimal with 25 ng/ml of thymosin fraction 5, it occurred within 6 h, and
it was completely inhibited by actinomycin D. The effect was specific in
that neither control nor spleen fraction 5- treated cells were induced to
express TdT. These data demonstrate that TdT expression in bone marrow
cells is under the direct control of thymic polypeptide hormones.
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