An investigation into the B lymphopoietic capacity of long-term bone marrow cultures.

A suspension of nucleated femoral (BALB/c x CBA) bone marrow cells was inoculated, either into glass flasks or into flasks coated with a preformed syngeneic marrow derived monolayer, and cultured for long periods in media supplemented with hydrocortisone sodium succinate. Long term analysis of the lymphoid status of these cultures was then carried out whilst they were producing CFU-S cells. The results show that T cells expressing the Thy 1 marker were present for up to 10 weeks, surface immunoglobulin positive (sIgM+) B cells were present for at least 6 weeks, whereas pre-B cells were present for no longer than one week. Pre-B, B and T cells were all present at levels well below those found in normal healthy bone marrow. When cultures were free of both B and pre-B lymphocytes, the cells collected from them were used to reconstitute lethally irradiated mice. Reconstitution was of the type (A x B) leads to A and approximately 2 months elapsed before reconstituted animals were analysed. The results show that despite the loss of pre-B cells from these cultures, precursors of B lymphocytes at earlier stages of differentiation were present for long periods, but were only capable of differentiation into sIgM+ B cells in vivo.