Ultrastructural study on long-term cultures of bone marrow cells with histamine-producing stimulating factor (HCSF).

In a previous study (Dy et al. 1981) we have demonstrated that histamine-producing cell stimulating factor (HCSF), a lymphokine released by T-cells, is present in supernatants obtained from secondary mixed lymphocyte cultures set up with cells from the donor and the recipient of a skin allograft, and that HCSF causes an increased production of histamine from target cells present in bone marrow. The most abundant source of target cells was found in the less dense layer of a discontinuous Ficoll gradient of bone marrow cells. Ultrastructural studies of this layer showed that it is composed of four types of cell: type I, immature cells; type II, mastocyte-like cells; type III, macrophages and type IV, lymphocytes. We have examined the effect of HCSF on this cell population; in long-term cultures we observed a progressive numerical decrease in type I cells, accompanied by an increase in type II cells (clearly observed as early as 48 h), leading to a pure population of mastocytes cells after 45 days of culture.