Expression of the Fc receptor in the mammary gland during lactation in themarsupial Trichosurus vulpecula (brushtail possum)

One of several functions described for the Fc receptor is regulation of IgG isotype transport into milk. The first marsupial homologues of the Fc rece ptor heavy and light chains, FcRn and beta -2 microglobulin, from the brush tail possum have been cloned and characterised. The level of FcRn mRNA in t he possum mammary gland was highest at the start of lactation, and decrease d slowly thereafter. Expression of FcRn mRNA did not increase during the sw itch phase when the concentration of IgG in milk is highest. In contrast, t he level of beta -2 microglobulin mRNA in the mammary gland increased durin g the switch phase when milk IgG concentration also increases. This correla tion between beta -2 microglobulin mRNA expression in the mammary gland wit h the time of active IgG-transfer into milk was also observed in the bovine and murine mammary gland. This suggests that expression of the Fc receptor in the mammary gland is controlled by the expression of beta -2 microglobu lin and that its expression is upregulated during the period of highest IgG -transfer into milk. (C) 2000 Elsevier Science Ltd. Ail rights reserved.