The Release of Granule Enzymes from Human Neutrophils Stimulated by Aggregated Immunoglobulins of Different Classes and Subclasses

Abstract Aggregated human myeloma proteins of subclasses IgG1, IgG2, IgG3, IgG4, IgA1, and IgA2 and normal IgG have been shown to react with human neutrophils in a serum-free medium and to induce release of the lysosomal enzyme β glucuronidase to the exterior of the cells. In contrast, IgD, IgE and IgM macroglobulins did not stimulate this release. Incubation of neutrophils with insoluble IgG and IgA aggregates resulted in adherence of the aggregates to the neutrophils and their phagocytosis. During this process, release of granule enzymes, but not of the cytoplasmic enzyme lactic dehydrogenase, occurred, indicating a selective process rather than one of cell lysis. Soluble aggregates did not induce liberation of enzymes when incubated with the neutrophils in suspension, but when bound to micropore filters to serve as nonphagocytosable surfaces, they stimulated adherent cells to release their granule contents. This latter process has previously been shown to result from direct extrusion of neutrophil granules to the exterior.