Monocytes do not inhibit peripheral blood erythroid burst forming unit colony formation.

To determine a possible role of peripheral blood monocytes in erythroid differentiation, various fractions of peripheral blood mononuclear cells were prepared from normal volunteers. The fractions contained 3-95% monocytes. These freshly prepared monocytes did not inhibit erythroid burst forming unit expression in plasma clot erythroid colony culture. Null cell preparations contaminated by up to 84% monocytes expressed erythroid burst forming unit colony formation when either T lymphocytes or T-cell conditioned medium was added. These results indicate that certain peripheral blood null cells engage the program of erythroid differentiation in the presence of T cells and erythropoietin. Monocytes do not inhibit this engagement.