Binding, internalization and degradation of soluble aggregates of human secretory IgA by resident rat peritoneal macrophages.

In the present study the in vitro binding, internalization and degradation of IgA immune complexes (IC) by phagocytes was studied. As a model for IgA IC, heat-aggregated human secretory IgA (AsIgA) was prepared and resident rat peritoneal macrophages (PM phi) were used as a source of phagocytes. First, binding of 125I-AsIgA to rat PM phi was investigated. Binding of 125I-AsIgA to PM phi at 4 degrees was saturable and reached plateau values after 2 hr. At 37 degrees, degradation of membrane-bound 125I-AsIgA into trichloroacetic acid (TCA)-soluble fragments occurred. Parallel experiments with unlabelled AsIgA and 125I-labelled anti-human IgA revealed that degradation of AsIgA was preceded by internalization of AsIgA. The specificity of binding of 125I-AsIgA to PM phi was investigated using human IgG, human serum IgA, human myeloma IgA1, human sIgA and the glycoproteins asialofetuin and ovalbumin. The binding of 125I-AsIgA to rat PM phi was inhibited in the presence of sIgA and asialofetuin. In contrast IgG and ovalbumin had no effect. These results suggest that receptors with a specificity for galactose on the rat PM phi are involved in the binding of AsIgA.