Inhibition of Neutrophil Oxidative Burst by Elastase-Generated IgG Fragments

Abstract

IgG1 is cleaved in vitro by granulocyte elastase into Fc, Fab and Fabc fragments. The cleaved products have been isolated by a series of chromatographic procedures and characterized with regard to molecular mass and isoelectric point. The Fc fragment has been previously shown to express at its N-terminal site a neoantigen which is specific for elastase (Kolb, G., Eckle, I., Heidtmann, H. H., Neurath, F. and Havemann, K. (1988) Scand. J. Rheumatol, S75, 179-189). The production of superoxide radical anions in prestimulated neutrophils is inhibited dose-dependently by the elastase-generated Fc and Fabc fragments. Native IgG1 and Fab fragments show no inhibitory effect, nor do papain-generated Fc fragments. The degree of inhibition depends on the stimulus applied: half-maximal inhibition is obtained by 6.mu.M Fc after stimulation with 4.beta.-phorbol and by 2,4.mu.M after stimulation with fMet-Leu-Phe: neutrophils stimulated with serum-activated zymosan are not inhibited by IgG fragments. The effect of Fc is purely cellular; no inhibition of O2 generation can be produced by applying Fc to the xanthine oxidase/xanthine system. The fragments have no effect on the activation or activity of crude NADPH oxidase, which is the O2--forming enzyme system of neutrophils. Possible mechanisms are discussed by which Fc acts on stimulated neutrophils.