Isolation of the receptor for IgG from a human monocyte cell line (U937) and from human peripheral blood monocytes.

Abstract

Fc receptors for IgG from a human monocyte [leukemia] line (U937) and from highly purified human peripheral blood monocytes were solubilized, purified and partially characterized. Both sources of cells gave indistinguishable results. Two molecules (or sets of molecules), one of about 72,000 MW [p72] and the other of 40,000-43,000 MW [p40-43], were discerned on autoradiograms of sodium dodecyl sulfate (SDS)-polyacrylamide gels, analyzing acid eluates from Sepharose-IgG columns over which detergent lysates of radioiodinated cells had been passed. The larger of the 2 molecules, p72, accounted for .gtoreq. 90% of the radioactivity. This component was heterodisperse both by size on SDS gels and by charge on isoelectric focusing gels. The charge heterogeneity, being virtually eliminated by neuraminidase and tunicamycin, was probably due to variable glycosylation. Several lines of evidence indicated that p72 is probably all or part of the Fc receptor: radiolabeling of this molecule using chloroglycouril was blocked by occupation by IgG of the Fc receptor; in soluble form this molecule expressed ligand specificity identical to the in situ receptor; the molecule was not recvered from affinity adsorbants bearing proteins that do not bind to the Fc receptors, nor from a human T cell line that does not bear Fc receptors. The smaller of the 2 molecules isolated, p40-43, is at least in part actin. Its relationship to p72 is not understood.