TISSUE-INJURY AND INFLAMMATION INDUCED BY IMMUNE-COMPLEXES - THE CRITICAL ROLE OF THE NEUTROPHIL LEUKOCYTE

Antigen-antibody or immune complexes when deposited into tissue of a neutropenic animal are inert causing no tissue damage or inflammation. The reaction in normal animals and man are entirely host mediated. Both complement and neutrophils play an essential role. By phagocytosing the immune complexes lysosomal enzymes are released from neutrophils and can cause damage, primarily to the microcirculation. Several proteases have been identified in neutrophils, of which elastase and collagenase can degrade various extracellular elements of connective tissue. Elastase in conjunction with cathepsin G (a chymotrypsin-like enzyme) degrade acticular cartilage. By acting on precursors (substrates) derived from plasma, vasoactive peptides and cleavage products of complement can be generated which induce vascular permeability and elicit chemotaxis. Thus, immune complexes can elicit, depending on their site of deposition, mild to severe tissue injury, culminating in the severe hemorrhagic lesions known as the Arthus reaction. The experimental lesions serve as models for a number of human diseases, which are believed to have a similar pathogenesis. The subject has been reviewed recently in detail (Ranadive and Movat, 1979). © 1979.