In vivo modulation of myelopoiesis by prostaglandin E2. III. Induction of suppressor cells in marrow and spleen capable of mediating inhibition of CFU-GM proliferation

Intravenous (IV) injection of 0.1 to 10 micrograms of authentic prostaglandin E2 (PGE2) in intact steady-state mice induces a population of bone marrow and spleen cells having the capacity to suppress CFU-GM proliferation when admixed with normal bone marrow cells. Equivalent suppression of CFU-GM committed to monocytic as well as granulocytic differentiation was observed using colony-stimulating factors (CSFs) differing in their lineage specificities and by direct morphological analysis of proliferating clones. Kinetic analysis indicates that suppressive bone marrow cells appear within 2 hours after PGE2 injection, are maximal at 6 hours, and are no longer observed by 24 hours postinjection. Positive and negative selection studies using monoclonal antibodies indicate that the PGE2-induced suppressor cells react positively with anti-GMA 1.2, MAC1, and F4/80 monoclonal antibodies, suggesting a myeloid/monocytic origin. As few as 1,000 positively selected bone marrow or spleen cells were able to inhibit maximally normal CFU-GM proliferation by 50,000 control bone marrow cells. Suppression of normal CFU-GM can be substituted for by 24- hour cell-free supernates from unseparated bone marrow cells or GMA 1.2 or F4/80 positively selected marrow or spleen cells from PGE2-treated but not control mice. These supernates also inhibited BFU-E proliferation. Injection of as few as 2 million bone marrow cells from PGE2-treated mice into steady-state mice or animals hematopoietically rebounding following a sublethal injection of cyclophosphamide significantly suppressed total CFU-GM proliferation in recipient mice within 6 hours. In summary, these studies describe the detection of a novel hematopoietic control network induced by PGE2 in intact mice.