Stimulation of neutrophil elastase and myeloperoxidase release by IgG fragments

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Abstract
SUMMARY: Human leucocyte elastase (HLE) cleaves IgG into Fab and Fc fragments. The Fc fragment bears an elastase-specific antigen and has previously been reported to be found in synovial fluid during rheumatoid arthritis, In addition, biological activity of clastasc-specific Fc fragments has been described in modulating granulocyte oxidative metabolism. To investigate further regulatory effects of the elastase-induced IgG cleavage products, we tested the elaslase and myeloperoxidase release of granulocytes. IgG fragments induce no enzyme release of unstimulated neutrophils. But elastase and myeloperoxidase release of cytochalasin b/FMLP-treated neutrophils is stimulated in a dose-dependent manner by the Fab fragments. The extent of stimulation depends on stimulus concentration and is at its maximum for low (e.g. 2.5 × 10−8m) FMLPconcentration. Ten nanomoles Fab/4 × 106 PMN augment elastase release to 206% and myeloperoxidasc release to 155% after prestimulation with 2.5 × 10−8 m FMLP. Fc fragments stimulate elaslasc release to 162% but no MPO release. Untreated IgGl and analog Fab and Fc fragments produced by papain cleavage react similarly. Elastase-generated IgG fragments may therefore up-regulate their concentration by stimulating elastase release. The concomitantly stimulated release of myeloperoxidase may influence bactericidal activity and termination of oxidative burst.