beta-Glucuronidase release from human monocytes induced with aggregated immunoglobulins of different classes

We studied beta-glucuronidase release from human monocytes induced with aggregated immunoglobulins of the nine different human classes and subclasses. Release was induced in a time and dose-dependent manner by all aggregated IgG subclasses. Aggregated IgA1 caused a greater beta-glucuronidase release than aggregated IgM, IgD, and IgE, but the difference was not statistically significant. Release of beta-glucuronidase was not phagocytosis dependent since inhibition of phagocytosis by cytochalasin B or dihydrocytochalasin B did not diminish enzyme release. On the contrary, cells incubated with cytochalasin B prior to addition of aggregated IgG released approximately twice as much enzyme compared to untreated controls. Enzyme release induced by latex particles, a non-Fc receptor mechanism, was decreased by cytochalasin B. Monomeric IgG1, IgG2, IgG3, and IgG4 inhibited aggregated IgG1 enzyme release in a dose-dependent manner. The ability of monomeric IgG to inhibit beta-glucuronidase release correlated with previous reports describing the binding affinities of monomeric IgG to monocytes, i.e., IgG2 was relatively ineffective compared to the other subclasses. Monomeric IgA, IgE, and pentameric IgM were unable to diminish IgG-induced enzyme release. The data indicate that normal peripheral blood monocytes express predominantly Fc receptors for IgG and that all four IgG subclasses induce the release of the lysosomal enzyme beta-glucuronidase.