Host-Mediated Regulatory Activities as Measured on Bone Marrow Cells Cultured in Diffusion Chambers and In Vitro

A suppressed granulopoiesis was found when murine bone marrow cells (BMC) and mature granulocytes were cocultured in intraperitoneally implanted diffusion chambers (DC) in normal mice. This inhibition was completely abolished when such DC cultures were transferred to new hosts during the culture period or implanted into endotoxin-injected or irradiated mice, but not when zymosan-injected mice were used. This host-mediated reversal of granulocyte inhibition correlated with changes in hematopoietic activities in DC fluid (DCF). Cell-free DCF was used either alone or in combinations with L-cell conditioned medium (L-CSF) or lung conditioned medium (LCM) in the in vitro assay. After colony counting, the in vitro cultures went through a washing procedure developed to measure the total cellularity of each culture dish and the differential distribution of cells in smears. Three activities were distinguished: (1) colony-stimulating activity; (2) enhancing activity on colony numbers and cell numbers both with L-CSF and LCM; and (3) a heat-labile factor which increased the fraction of granulocyte colonies.