B lymphocyte and macrophage expression of carcinoembryonic antigen‐related adhesion molecules that serve as receptors for murine coronavirus

The expression of carcinoembryonic antigen (CEA)‐related glycoproteins that have been associated with intercellular adhesion and that serve as receptors for mouse hepatitis virus (MHV) was analyzed in cells from the immune system of BALB/c mice using immunolabeling and RNA polymerase chain reaction amplification of receptor transcripts. These glycoproteins, which are called biliary glycoproteins, were highly expressed in B lymphocytes, including cells of the B‐la (CD5⁺) lineage, and in macrophages, but were not detectable in resting T lymphocytes. Similarly, murine cell lines of B cell and macrophage origin expressed messenger RNA encoding CEA‐related molecules, while the corresponding mRNA was only slightly detectable in a T cell line. These CEA‐related cell adhesion glycoproteins were also expressed in endothelial cells. Therefore, their specific interaction with their so far unknown ligand may be of functional importance in cellular interactions in the immune response. Monoclonal antibody directed against these glycoproteins blocked MHV‐A59 infection of the B cell‐derived SP20 cell line. Thus, the functional receptors for MHV on B lymphocytes, like those on murine fibroblasts, are isoforms of CEA‐related glycoproteins. Treatment of B cells with anti‐receptor antibody also blocked B cell‐mediated cytotoxicity against MHV‐A59‐infected fibroblasts, indicating that this phenomenon is mediated by interaction of viral attachment protein on the infected target cells with specific CEA‐related receptor glycoproteins on the effector B cells.