Cytophilic Properties of IgA to Human Neutrophils

Abstract

In 1961 Boyden and Sorkin demonstrated that antigens can be bound to spleen cells which have previously been incubated with specific antisera (1). The term “cytophilic” immunoglobulins was coined for this type of antibody. Subsequently, it was shown that immunoglobulins attach via the Fc fragment to receptors on phagocytic cells such as macrophages (2,3), monocytes (4) and neutrophils (5). The biological importance of the cytophilic antibodies appears to be promotion of phagocytosis (opsonization) of antigens. Not all immunoglobulins are cytophilic. In rodents, IgG of slow electrophoretic mobility, γ2G, is cytophilic whereas γ1G, the anodally migrating IgG is not (3). In man, it has been shown by inhibition studies that IgG1 and IgG3 are cytophilic for monocytes (4) and neutrophils (5). Most of these findings were made by studying “rosette” formation, that is the adherence of antibody coated red cells to phagocytes (3,4,5). More recently, cytophilic properties have also been studied by measuring the uptake of radiolabeled immunoglobulins on macrophages (6) or by release of histamine from basophils (7). Relatively little is known about cytophilic properties of IgA, probably because it is difficult to obtain pure IgA antibodies suitable for cytophilic testing. Since the cytophilic reaction depends on the Fc fragment, immunoglobulins having no demonstrated antibody activity such as myeloma proteins can also be used as a source of IgA. Isolated IgA myeloma proteins were therefore used in this study. First, the release of lysosomal enzymes from neutrophils following incubation with aggregated IgA was analyzed (8) and second, the uptake of radiolabeled IgA onto neutrophils was measured and compared to that of other immunoglobulin classes (9).