Human macrophage-like cell line U937-1 elaborates mitogenic activity for fibroblasts

The human macrophage-like cell line U937-1 was shown to elaborate mitogenic activity for cultured fibroblasts. Activity was present in the culture medium when cells were maintained either in the presence or absence of serum components, although maximal levels were observed when the macrophage-like cells were incubated in medium supplemented with platelet-poor plasma. The mitogenic activity acted synergistically with platelet-poor plasma to allow density-arrested cells to initiate DNA synthesis and its action was potentiated by the addition of cholera toxin. The elaborated activity bound to DEAE Sephacel and was eluted in a single peak using an NaCl gradient.