In vivo modulation of myelopoiesis by prostaglandin E2. IV. Prostaglandin E2 induction of myelopoietic inhibitory activity.

Conditioned medium (CM) prepared from bone marrow (BM) or spleen (SPL) cells from mice injected with PGE2 in doses ranging from 0.0001 to 10 micrograms was found to contain an activity inhibitory to the proliferation of granulocyte-monocyte progenitor cells (CFU-GM). This activity was found in medium conditioned for 24 to 48 h, but was not present in medium conditioned for longer time intervals. BM cells from PGE2-treated mice incubated over a concentration range of 0.1 to 1.0 x 10(6) cells/ml and SPL cells over a range of 1.0 to 10 x 10(6) cells/ml produced CM with equivalent degrees of inhibition for CFU-GM proliferation. Titration of this activity revealed a significant inhibitory effect still present at a 1/256 dilution. Inhibitory activity was similar whether or not CM was prepared in the presence or absence of FCS. Inhibition of CFU-GM development was approximately equal in the presence of either PWM SPL CM or L cell CM as sources of CSF activity. Morphologic analysis of CFU-GM revealed an equivalent inhibition of monocyte, monocyte-neutrophil, and neutrophil CFU-GM by the PGE2-stimulated inhibitory activity. Equivalent picogram amounts of PGE were measured in CM derived from BM or SPL cells from either control or PGE2-treated mice, indicating a low probability that injected PGE2 was carried over in the CM and contributed to CFU-GM inhibition. Protease digestion of BM or SPL cell CM from PGE2-treated mice revealed a loss of inhibitory activity after trypsin, chymotrypsin, pronase, and neuraminidase treatment. Inhibitory activity was also ablated by heat treatment at 56 degrees C for 30 min and 100 degrees C for 5 min. Acrylamide-agarose gel filtration of BM CM revealed an active inhibitory fraction in the Mr range of 5.5 to 8.0 kDa. The results of the present study suggest that one of the mechanisms by which PGE2 exerts its in vivo myelopoietic inhibitory action may be by stimulating the production of an inhibitory factor or factors from BM and SPL cells.