Role of pokeweed mitogen spleen conditioned medium in regulating haematopoiesis in long-term human marrow cultures.

The modulatory effect of pokeweed mitogen spleen conditioned medium (PWM-SCM) on the growth of myeloid progenitors (CFU-C) and on the composition of the stromal layer in human bone marrow long-term cultures was studied. In the presence of PWM-SCM there was enhanced CFU-C growth in the adherent layer throughout 6 weeks of incubation, with 2-fold, 2-fold and 3.4-fold increases during wk 2, 4 and 6 respectively (p less than 0.05). In the non-adherent layer of control cultures, however, there was a rapid decline in haematopoiesis which could not be offset by PWM-SCM. The differentiation pattern of CFU-C (entailing monocyte - macrophage progenitors CFU-M, granulocytic progenitors CFU-G or monocyte - granulocyte progenitors CFU-GM) was not altered by PWM-SCM. Fewer lipid-containing cells developed in the adherent layer of cultures treated with PWM-SCM than in control cultures, but the distribution pattern of monocytes - macrophages or granulocytes was not affected. These results suggest that in long-term cultures of human marrow cells there may be extensive haematopoiesis in the presence of PWM-SCM. Whether this is a direct effect on progenitor cells of stimulating factors, or rather of accessory cells in the adherent layer, remains to be clarified.