Calnexin and ERp57 facilitate the assembly of the neonatal Fc receptor for IgG with beta 2-microglobulin in the endoplasmic reticulum.

The neonatal FcR (FcRn) consists of an MHC class I-like H chain in noncovalent association with beta(2)-microglobulin (beta(2)m). The proper folding of FcRn in the endoplasmic reticulum is essential for FcRn function. Using a low stringency immunoprecipitation of human FcRn, we observed the coprecipitation of an 88-kDa band.