Dual biological function of a T-cell-derived murine immunoenhancing factor.

Murine enhancing factor (MEF), derived from the culture fluid of mixtures of histoincompatible spleen cells, was found to have two apparently different, but perhaps closely related, biological activities. First, MEF can functionally replace T cells in nonspecifically augmenting the anti-sheep erythrocyte plaque-forming cell response of T-cell-depleted, mouse splenic B-cell cultures. Second, the mediator acts similarly to colony stimulating factor from human urine in promoting the formation of colony-forming units (CFU) in soft agar bone marrow cell cultures. This latter function of MEF was manifest in the absence of detectable increases in the level of incorporation of ³H]thymidine by cultured bone marrow cells. Morphologically, the cells comprising the CFU were macrophage-like in appearance. The data suggest that MEF may function as a differentiation signal for the maturation of antigen-activated B lymphocytes into immunoglobulin-secreting cells, as well as for the modulation of hematopoietic or granulopoietic macrophage stem cells into mature, functional macrophages.