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Splenic plaque-forming cells (PFC) and stem cells (CFU-s) during acute phenylhydrazine-induced enhanced erythropoiesis.

The erythroid status and levels of splenic plaque-forming cells (PFC) to sheep red blood cells (SRBC) were monitored in mice subsequent to acute phenylhydrazine (PHZ)-induced hemolytic anemia. From ferrokinetic measurements, we noted a shift in erythropoiesis from bone marrow to spleen. The levels of splenic PFC were significantly depressed following PHZ-induced erythroid differentiation. Although this immune depression may reflect competition at the stem cell levels, whereby pluripotent stem cells (CFU-s) are preferentially differentiated into the erythroid line at the expense of lymphopoietic pathways, other possibilities cannot be excluded. In this regard, we have shown that loading of the mononuclear phagocyte system (MPS) by PHZ-damaged erythrocytes effected profound depressions in splenic PFC numbers. Lastly, in addition to the well-documented increases in CFU-s migration from marrow to spleen during enhanced erythropoiesis, we noted increased migration of B lymphocytes (as assessed by PFC) in marrow-shielded lethally-irradiated mice given PHZ. We also provide data which show that PHZ-damaged RBC evoke increased migration of CFU-s in normal mice, indicating a possible involvement of the MPS in stem cell migration.