Expression of 20 alpha-hydroxysteroid dehydrogenase in the mouse marrow cells: strain differences, thymic effect on enzymatic activity, and possible localization in pre T lymphocytes.

The enzyme 20 alpha-hydroxysteroid dehydrogenase (20 alpha SDH) was studied in bone marrow cells from various strains. The bone marrow cells of congenitally athymic (nude) and normal BALB/C mice consisted of 2 subpopulations of nucleated cells, larger cells of 10-14 microns and smaller cells of 7 microns in size. About 75% of the 20 alpha SDH activity was located in the larger cells. Bone marrow cells from young neonatally thymectomized or congenitally athymic mice had an increase portion of big cells and contained twice as much 20 alpha SDH activity as control mice. Liver cells from 1-day-old mice and spleen cells from mice lethally irradiated and bone marrow reconstituted, both of which contained primarily stem cells, erythroid, myeloid and pre B lymphocytes, had essentially no 20 alpha SDH. Following stimulation with PHA marrow cells from athymic nude mice responded to the mitogen in terms of [3H]thymidine incorporation and stimulation of 20 alpha SDH activity. Bone marrow cells after stimulation with PHA were labelled with fluorescein conjugated anti-theta antibodies. With the aid of fluorescence activated cell sorter (FACS II) it was found that the fluorescent cells had 2.5-5 fold more 20 alpha SDH activity than the unlabelled cells. The results support the suggestion that the 20 alpha SDH activity is located in the marrow pre T lymphocytes.