Lysosomal enzyme release from polymorphonuclear leukocytes induced by immune complexes of IgM and of IgG.

Lysosomal enzyme release by rabbit polymorphonuclear leukocytes induced by immune complexes of IgM or IgG antibodies and ovalbumin was studied by in vitro experiments. It was shown that IgM immune complexes in the form of precipitates were able to stimulate the release of the lysosomal enzymes beta-glucuronidase and alkaline and acid phosphatases, in contrast to heat-aggregated IgM, which had only a small effect. This stimulation was dependent on the presence of Ca2+ in the extracellular medium; Mg2+ showed a slight effect as a substitute for Ca2+. IgG precipitated immune complexes prepared from different regions of the precipitation curve were tested. It was shown that immune precipitates from the equivalence region were the most effective; those at antibody excess have a smaller but comparable capacity, whereas the precipitated immune complexes at antigen excess were the least effective. Soluble immune complexes of IgG with an excess of antigen concentration in the range of 2.5 to 5 times that of equivalence were also able to stimulate the enzyme release, but that capacity decreased rapidly with the increase in antigen concentration. The enzyme release induced by IgM immune complexes was not inhibited by competition with free immunoglobulin in the medium, either IgM or IgG in approximate physiologic concentrations; contrarily, with IgG immune complexes, free monomeric IgG (but not IgM) can completely block the process. The possible implications of these findings in the immune complex diseases are discussed.