Surface phenotype analysis of human monocyte to macrophage maturation

Cells of the mononuclear phagocyte system arise from circulating blood monocytes. Upon emigration from the vasculature, monocytes differentiate into macrophages, a pro-cess that monocytes similarly undergo in vitro. We have established primary cultures from elutriated or adherence-purified blood monocytes and analyzed the antigenic mod-ulation during monocyte to macrophage transformation, which could be followed by the expression of specific antigens and which required as yet unknown inducer signals present in the serum. It is shown that in the absence of serum monocytes only survive in vitro when cultured adherent to plastic but rapidly die in suspension culture. Starting at 0.5%, serum induced maturation dose-dependently, with the optimal concentration being 2 to 5%. of those antigens not present on monocyte, the low-affinity Fc receptor (CD1 6), the ca-chain of the vitronectin receptor (CD51), gp65-MAX.1, and gp68-MAX.3 were ex-pressed only upon serum-induced macrophage differentiation, whereas the transferrin receptor (CD71), MAX.26, and to some degree also gp65-MAX.11 appeared to be inde-pendent of maturation and were also found on primary cultures of adherent monocytes under serum-free conditions. In addition, the rapid induction of HLA class II antigen