TISSUE AND CELLULAR-DISTRIBUTION OF AN ADHESION MOLECULE IN THE CARCINOEMBRYONIC ANTIGEN FAMILY THAT SERVES AS A RECEPTOR FOR MOUSE HEPATITIS-VIRUS

BACKGROUND: The receptor for the murine coronavirus mouse hepatitis vi rus (MHV)-A59, called MHVR or Bgp1(a), is a glycoprotein in the carcin oembryonic antigen family of the Ig superfamily. Biliary glycoprotein (Bgp) isoforms play a role in cell adhesion, bile acid transport, and ecto-ATPase activity. MHV-resistant SJL/J mice express a different all ele of Bgp1 called Bgp1(b). Analysis of the tissue and cellular distri bution of Bgp1 proteins can therefore provide new insight on both cell ular functions and MHV-A59-induced pathogenesis. EXPERIMENTAL DESIGN: Bgp1 expression was analyzed in the digestive, respiratory, endocrine, urinary, and central nervous systems of adult BALB/c and SJL/J mice b y immunocytochemistry and immunoelectron microscopy using a monoclonal Ab specific for the N terminal domain of the Bgp1(a) proteins and pol yclonal rabbit anti-Bgp1, which recognizes both the Bgp1(a) and Bgp1(b ) proteins. The function of Bgp1 proteins as viral receptors was teste d on tissue sections by a virus binding assay. MHV-A59 replication was analyzed by immunocytochemistry. RESULTS: Bgp1 expression was observe d on membranes of epithelial cells (including hepatocytes, intestinal, endocrine, and respiratory epithelial cells), kidney proximal tubules , and endothelial cells in many tissues. It was usually localized at t he apical pole of the cells and, when present, on the brush borders an d the cilia. A new direct virus binding assay showed that MHV attachme nt onto cells correlates with Bgp1 expression. Viral infection was det ected in hepatocytes, lymphoid tissue, and the exocrine pancreas but n ot in endocrine cells, enterocytes, kidney, or respiratory cells. In t he central nervous system, no immunolabeling of neurons or glial cells was found with anti-Bgp1 Ab. CONCLUSIONS: Bgp1 proteins are present o n BALB/c and SJL/J epithelia and endothelia. These glycoproteins might be involved in cell-to-cell contacts, for example between hepatocytes . On BALB/c mice, Bgp1(a) expression is consistent with the tropism of MHV-A59 for the liver. However, Bgp1(a) was also expressed on cells t hat were not infected by MHV-A59.