In addition to the spike (S)
glycoprotein that binds to
carcinoembryonic antigen-related receptors on the host cell membrane, some strains of mouse coronavirus (mouse hepatitis virus [MHV]) express a
hemagglutinin esterase (HE)
glycoprotein with hemagglutinating and
acetylesterase activity. Virions of strains that do not express HE, such as MHV-A59, can infect mouse fibroblasts in vitro, showing that the HE
glycoprotein is not required for
infection of these cells. The present work was done to study whether interaction of the HE
glycoprotein with
carbohydrate moieties could lead to virus entry and
infection in the absence of interaction of the S
glycoprotein with its receptor
glycoprotein, MHVR. The DVIM strain of MHV expresses large amounts of HE
glycoprotein, as shown by hemadsorption,
acetylesterase activity, and immunoreactivity with
antibodies directed against the HE
glycoprotein of bovine coronavirus. A monoclonal anti-MHVR antibody, MAb-CC1, blocks binding of virus S
glycoprotein to MHVR and blocks
infection of MHV strains that do not express HE. MAb-CC1 also prevented MHV-DVIM
infection of mouse DBT cells and primary mouse glial cell cultures. Although MDCK-I cells express O-acetylated
sialic acid residues on their plasma membranes, these canine cells were resistant to
infection with MHV-A59 and MHV-DVIM. Transfection of MDCK-I cells with MHVR
cDNA made them susceptible to
infection with MHV-A59 and MHV-DVIM. Thus, the HE
glycoprotein of an MHV strain did not lead to
infection of cultured murine neural cells or of nonmurine cells that express the
carbohydrate ligand of the HE
glycoprotein. Therefore, interaction of the spike
glycoprotein of MHV with its
carcinoembryonic antigen-related receptor
glycoprotein is required for infectivity of MHV strains whether or not they express the HE
glycoprotein.