An immunofluorescence study of IgG receptors in rodent enterocytes.

Locations of IgG receptors in the small intestine of suckling rats were visualized by treating sections of the gut with IgG and FITC-labelled anti-IgG antibodies. Receptors, operative optimally at acid pH, occurred only in younger rats whose intestines were still permeable to antibodies; they were located on the brush borders of the enterocytes on the apical parts of the villi in the duodenum and jejunum. Premature disappearance of the receptors from the gut was achieved by cortisone treatment. In rats and mice, IgG from different species each competed for attachment to the receptors in vitro in the same way as it inhibited the transmission of other IgG across the intestine in vivo, thus reflecting the involvement of the receptors in the transport mechanism.