Characterization and localization of the neonatal Fc receptor in adult human kidney.

The binding of Fc fragments of Ig on glomerular epithelial cells (GEC) was observed previously, but the receptor could not be identified. In immunofluorescence and immunohistochemical studies using normal adult human kidney sections, the presence of the so-called neonatal Fc receptor (FcRn) was demonstrated on GEC as well as in the brush border of proximal tubular cells. FcRn transcripts were also detected on isolated glomeruli by reverse transcription-PCR. Using an immortalized GEC line, the presence of the FcRn was confirmed by flow cytometry, reverse transcription-PCR, Western blotting, and by the pH dependence of the binding of heat-aggregated IgG. Because it is well established that the FcRn is involved in IgG transcytosis, it is hypothesized that the FcRn in the kidney may play a role in the reabsorption of IgG. Ongoing studies should clarify the role of the FcRn as a potential target for immune complexes on GEC and should assess its relevance in physiology and pathology.