Two stages of increased IgA transfer during lactation in the marsupial, Trichosurus vulpecula (brushtail possum)

The polymeric Ig receptor (pIgR) and J chain molecules are involved in the transfer of IgA across the mammary gland epithelia into milk. The J chain h inds two IgA molecules to form dimeric IgA, and the pIgR transports this co mplex through epithelial cells. We report here the cloning of the first mar supial homologues for the pIgR and J chain from the brushtail possum, Marsu pial young are born after a short gestation and are less developed than eut herian newborn. The pouch young is completely dependent on milk as its sole source of nutrition during; early lactation and this phase can be consider ed to be equivalent to an external gestation. Two periods of increased expr ession of pIgR, J chain, and IgA heavy chain mRNAs were observed in the mam mary gland during lactation. The first occurs for a brief period after birt h of the pouch young and is likely to reflect IgA transfer via the colostru m. The second period of increased expression, which is unique to marsupials , occurs after the early lactation period and just before young exit the po uch. We propose that this represents a second colostral-like phase at the e nd of the external gestation.