The murine pregnancy-specific glycoprotein-16 (PSG16; previously brain carcinoembryonic antigen/bCEA) is expressed in the brain, especially in neurons, and has previously been reported to be an MHV receptor. The murine pregnancy-specific glycoproteins (PSGs), which mediate placentation and modulate interactions between the fetus and the maternal immune system, resemble the related carcinoembryonic antigen (CEA) proteins in their extracellular Ig-like domains but are secreted rather than membrane-anchored.