Metabolic heterogeneity among human monocytes and its modulation by PGE₂

Human peripheral blood monocytes (M∅) were fractionated on a discontinuous bovine serum albumin density gradient, and cells from each fraction was assayed for their specific activity of two enzymes, which represent correlates of M∅ activation or differentiation (5'-nucleotidase, acid phosphatase) and their synthesis of prostaglandin E₂ (PGE₂). On the basis of significant differences in these parameters, the monocytes could be divided into two broad populations. Low density cells demonstrated low specific activities of 5'-nucleotidase (5'N), high specific activities of acid phosphatase (APT'ase), and synthesized substantial amounts of PGE₂. In contrast, high density cells demonstrated high specific activities of 5'-N, low specific activities of APT'ase, and synthesized meager amounts of PGE₂. To determine if these biochemical differences served as stable markers of M∅ subpopulations, low and high density M∅ were individually cultured for 3 days, and changes in the metabolic parameters were assayed. Although 5'-N and APT'ase, increased among each population, the magnitude of this change could be modulated by PGE₂. When each population was cultured in a concentration of PGE₂ equivalent to that synthesized by the whole M∅ differences in 5'-N and APT'ase, remained as useful discriminators of the M∅ subpopulations. The pertinence of these findings to events involved in M∅ activation and differentiation as well as a possible role for PGE₂ in modulating these events is discussed.