Abstract
We have utilized monoclonal antibodies against the two IgG Fc receptors (p40 and p72) of U937 cells to stimulate the release of superoxide. The monoclonal antibody (mAb) specific for p40 (IV3) has been described elsewhere. A murine IgG1 mAb specific for the high affinity p72 Fc receptor (designated mAb FcR32 or simply mAb 32) bound to the same p72 precipitated by Sepharose-human IgG as shown by preclearing experiments and by identical isoelectric focussing patterns. Binding of mAb 32 to p72 was independent of the Fc region of the antibody since Fab' fragments of mAb 32 affinity adsorbed p72. The binding of both mAb 32 and human IgG1 to the intact U937 cell was not reciprocally inhibitory, indicating that mAb 32 does not interfere with the ligand binding site of p72. mAb 32 bound to human monocytes, U937, and HL60 cells, but not to granulocytes or lymphocytes. U937 cells cultured in gamma-interferon and 1,25-dihydroxycholecalciferol generated superoxide when incubated with mAb 32 or IV3 followed by cross-linking with F(ab')2 anti-murine Ig. Incubation with mAb 32 or IV3 alone or with 3 of 5 other anti-U937 mAbs cross-linked with anti-murine Ig did not result in superoxide generation. Immune complex-mediated superoxide production was inhibited 80% by IgG, but not by mAb 32 or IV3.
Highlights
From the Departments of Medicine, Pediatrics, Pathology, Microbiology,and the Cancer Center, University of Rochester Medical Center, Rochester, New York 14642 and the Departments of Microbiology and Physiology,Dartmouth Medical School, Hanouer, New Hampshire 03756
Binding of mAb 32 to p72 was independent of the Fc region of the antibody since Fab‘ fragments of mAb 32 affinity adsorbed p72. The binding of both mAb 32 andhuman IgGl to the intact U937 cell was not reciprocallyinhibitory,indicating that mAb 32 does not interfere with the ligand binding site of p72. mAb 32 bound to human monocytes, U937, and HL60 murine IgG
Any assay for Fc receptor binding would register all antibodies of these two subclasses
Summary
The monoclonal inhibits ligand binding[1].This receptor is present antibody (mAb) specific for p40 (IV3) has been de- on mononuclear phagocytes, but on human platelets, neutroscribed elsewhere. The 72-kDa Fc receptor mediates murine IgG2a anti-T3-induced stimulation,whereas the 40-kDa Fc receptor mediates murine IgGl anti-T3-induceTd cell mitogenesis [1] Based upon their distinctive affinities for murine IgG subclasses, p72 and p40 are thought to be the humhoamn ologues of murine macrophage Fcreceptor I and Fcreceptor I1specific for murine IgGZa and IgG2b/l, respectively [8, 9]. Monoclonal antibody specific for the 72-kDahigh affinity Fc. Immune complex-mediated superoxide production was receptor and show that cross-linkingof monoclonal antibodies inhibited 80%by IgG, but not by mAb 32 orIV3. $ T o whom correspondence and reprint requests should be addressed Ohio State University, 456 Clinic Dr, Rm. 4715, Columbus, OH 43210
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