Biochemical properties of macrophage fractions and their relation to the mechanism of superoxide production.

Guinea pig alveolar macrophages are separable by density gradient centrifugation into three subpopulations whose capacity for biological activity (e.g. O2- production and chemotaxis) varies directly with buoyant density [(1983) J. Reticuloendothel. Soc. 33, 157-164]. This study demonstrates that the activity per cell of various other enzymes remains constant among the subpopulations. When normalized for cell volume, enzyme activity diminishes with decreasing buoyant density. Intracellular calcium mobilization, linked to formyl peptide and concanavalin A-stimulated O2- production, similarly diminishes. Formyl peptide receptor distribution and affinity remain constant. Decreased responsiveness of lower density cells is probably due to lower concentration of enzyme(s) involved in the transduction of signal distal to ligand recognition (or binding).