Distribution of rat neonatal Fc receptor in the principal organs of neonatal and pubertal rats.

The neonatal Fc receptor (FcRn) mediates the transfer of IgG and albumin, also protects them from catabolism. This study characterized the expression of FcRn in different organs of neonatal and pubertal rats by reverse transcription-PCR (RT-PCR) and immunohistochemistry, demonstrates that FcRn is expressed in liver, kidney, intestine, heart, lung, spleen, skin and skeletal muscles at varying levels post-gestation from d 1 to d 63. This finding is contrary to previous studies claiming that FcRn is undetectable in most tissues after weaning. Lungs were the predominant organs for FcRn expression, whereas skin, liver and intestine are considerably less expressed organs. The expression of FcRn fluctuated in all the organs tested, and with a higher frequency before weaning compared to puberty. These findings may provide clues for the better understanding of FcRn function, and are important for determining the dosage levels for IgG and the constant region fragment (Fc)-containing therapeutic proteins whose half-life is regulated by FcRn.