A flow microfluorimetric analysis of the binding of immunoglobulins to Fc gamma receptors on brush borders of the neonatal mouse jejunal epithelium.

In order to determine whether the neonatal mouse small intestine has the ability to be selective in the binding of homologous immunoglobulin isotypes, mouse immunoglobulins were tested for their ability to bind to brush borders isolated from jejunal enterocytes of neonatal and adult mice. The binding of immunoglobulins to brush borders was detected by fluorescence-activated cell sorter (FACS) analysis. The results showed that brush borders from 12-day-old mice bound mouse immunoglobulins selectively, binding IgG2a, IgG2b, IgG3 and IgE but not IgG1, IgM or IgA. Similarly, at 16 days, only IgG2a, IgG2b, IgG3 and IgE were bound significantly. The ability of jejunal brush borders to bind gamma-globulins declined with age and their selectivity was lost such that in mice of 18 days and over not one of the immunoglobulins tested was bound. It was concluded that neonatal mouse jejunal Fc gamma receptors bind IgG2a and IgG2b almost exclusively. The sudden drop in binding between 16 and 18 days coincides with the previously reported age at which immunoglobulin transmission across the gut in the neonatal mouse ceases (closure).