Functional heterogeneity of macrophages

The antibody-binding activities of rabbit peritoneal macrophages separated on discontinuous gradients of Ficoll were investigated. The antibody was rabbit anti-ovalbumin IgG labelled with 125I. Of the five fractions obtained, one macrophage fraction was found to bind substantially more antibody than the others. These macrophages possessed more Fc receptor sites than the others and the number of Fc receptors (n) and the association constant (K) of these cells was calculated. By electron microscopy, the phagocytic activity of the subpopulation with most Fc receptors was less than that of the others.