Expression of FcRn, the MHC Class I-Related Receptor for IgG, in Human Keratinocytes

Abstract

The neonatal Fc receptor (FcRn) for IgG has been shown to be responsible for IgG transport and to be involved in IgG catabolism. In this study, we show expression of FcRn in normal human epidermal keratinocytes. By RT-PCR, we demonstrate the FcRn alpha-chain mRNA obtained from cultured keratinocytes creating a 457 bp product as confirmed by sequence analysis. Northern blot analysis shows a 1.5 kb transcript. Real-time PCR reveals consistent expression of FcRn alpha-chain mRNA in human keratinocytes from different donors. Anti-FcRn alpha2-extracellular domain and anti-FcRn cytoplasmic tail antibody (Ab) directed against defined antigenic targets were generated and used for immunoblotting and immunoprecipitation revealing protein expression of the 46 kDa FcRn alpha-chain. By immunofluorescence microscopy, we find granular-vesicular staining for FcRn alpha-chain in keratinocytes. Fluorescence-activated cell sorting analysis gives predominantly an intracellular distribution of FcRn in keratinocytes. Biochemically, we demonstrate Fc-dependent binding of human IgG at acidic pH. In normal human epidermis, we find a cytoplasmic vesicular staining of predominantly basal and suprabasal keratinocytes. In summary, we demonstrate expression of a functional FcRn in normal human epidermal keratinocytes. These findings further emphasize the role of keratinocytes as immunomodulating cells in inflammatory and immunologic processes of the skin.

The effect of the neonatal Fc receptor on human IgG biodistribution in mice

“…Based on our current results, and the observed various tissue distribution pattern changes in FcRn KO mice, we believe it is more likely that FcRn also play roles in transporting antibody into, or out of, specific organs. This is consistent with the reported widespread expression of FcRn in tissues, including the liver, 18 bone marrow, 19,20 lungs, 21 kidneys, 10,22 skin, 23,24 and spleen. 25 For example, the T/B ratios of IgG1 in the liver and spleen were higher in FcRn KO mice across all time points.…”

Neonatal FcR Expression in Bone Marrow-Derived Cells Functions to Protect Serum IgG from Catabolism

“…The stratum corneum and epidermis of mouse skin also stained weakly with the antiserum (Fig. 3A), consistent with a previous report (28). However, this staining was nonspecific as a similar pattern of staining was seen in FcRn knockout skin.…”

“…Even though the mouse is the most commonly used mammalian model organism, the tissue expression pattern of FcRn expression in mouse had not been previously examined. Most published studies used rat or human tissues (19,21,22,28,33,34,40,41). The availability of FcRn-deficient animals (3) allowed us an important control for staining specificity.…”

Tissue expression profile of human neonatal Fc receptor (FcRn) in Tg32 transgenic mice

“…FcRn measurements in some selected tissues have previously been carried out via ligand binding assay, 17 protein immunoblotting, 17,30 tissue staining, 31 or transcriptional analysis from various cultured cell types. 32 However, to the best of our knowledge, systematic quantification of FcRn across tissues has not been reported, which is likely due to the technical challenges associated with tissue-based bioanalysis of membrane proteins.…”