Persistent infection promotes cross-species transmissibility of mouse hepatitis virus

Persistent infection with mouse hepatitis virus (MHV) strain A59 in murine DBT (delayed brain tumor) cells resulted in the emergence of host range var iants, designated V51A and V51B, at 210 days postinfection, These host rang e mutants replicated efficiently in normally nonpermissive Chinese hamster ovary (CHO), in human hepatocarcinoma (HepG2), and to a lesser extent in hu man breast carcinoma (MCF7) cell lines. Little if any replication was noted in baby hamster kidney (BHK), green African monkey kidney (COS-7), feline kidney (CRFK), and swine testicular (ST) cell lines. By fluorescent antibod y (FA) staining, persistent viruses V10B and V30B, isolated at days 38 and 119 days postinfection, also demonstrated very low levels of replication in human HepG2 cells. These data suggest that persistence may rapidly select for host range expansion of animal viruses. Pretreatment of HepG2 cells wit h a polyclonal antibody directed against human carcinoembryonic antigens (C EA) or with some monoclonal antibodies (Col-1, Col-4, Col-12, and Col-14) t hat bind human CEA significantly inhibited V51B infection, Under identical conditions, little or no blockade was evident with other monoclonal antibod ies (kat4c or Col-6) which also bind the human CEA glycoproteins, In additi on, an antibody (EDDA) directed against irrelevant antigens did not block V 51B replication. Pretreatment with the Col-4 and Col-14 antibodies did not block Sindbis virus replication in HepG2 cells or MHV infection in DBT cell s, suggesting that one or more CEA glycoproteins likely functioned as recep tors for V51B entry into human cell lines. To test this hypothesis, the hum an biliary glycoprotein (Bgp) and CEA genes were cloned and expressed in no rmally nonpermissive BHK cell lines by using noncytopathic Sindbis virus re plicons (pSinRep19), By growth curves and FA staining, human CEA and to a m uch lesser extent human Bgp functioned as receptors for V51B entry. Further more, V51B replication was blocked with polyclonal antiserum directed again st human CEA and Bgp, Under identical conditions, the parental MIN strain A 59 failed to replicate in BI-IK cells expressing human Bgp or CEA, These da ta suggest that MHV persistence may promote virus cross-species transmissib ility by selecting for virus variants that recognize phylogenetic homologue s of the normal receptor.