20α-Hydroxysteroid Dehydrogenase: A T Lymphocyte-Associated Enzyme

Open Access
Publisher Website
Google Scholar
Abstract
20α-Hydroxysteroid dehydrogenase (20α-SDH), an enzyme which reduces progesterone to 20α-dihydroprogesterone, was found to be associated with T lymphocytes. 20αSDH activity was present in spleen cells bearing θ antigen, spleen cells nonadherent to nylon wool (T lymphocyte-enriched population), and in thymocytes. Almost no enzymatic activity was found in bone marrow cells from normal mice and in spleen cells from neonatally thymectomized or athymic nude mice. T cell mitogens (PHA and Con A), but not the B cell mitogen LPS, induced high levels of enzymatic activity 48 hr after addition to spleen cell cultures. The level of 20αSDH activity in lymphocytes was age dependent. At the age of 4 weeks 20αSDH activity in thymocytes, spleen cells, and lymph node lymphocytes was 3 to 5 times higher than at 8 and 16 weeks. Progesterone (5.0 × 10-7 M) was found to inhibit thymocyte proliferation after exposure to mitogens, but not 20α-dihydroprogesterone (10-6 M). 20α SDH may protect the embryonic thymocytes against high concentrations of progesterone.