Infection of polarized epithelial cells with enteric and respiratory tract bovine coronaviruses and release of virus progeny.

OBJECTIVE: To investigate the susceptibility of polarized epithelioid human rectal tumor (HRT-18G) cells to bovine coronaviruses (BCV) isolated from enteric (EBCV) and respiratory (RBCV) tract infections. PROCEDURE: Cells of the G clone of HRT-18 were grown to confluent monolayers on permeable supports, and were directionally infected at the apical and basolateral domains with 3 wild-type BCV strains, RBCV-LSU-94LSS-051-2, RBCV-OK-0514-3, and EBCV-LY138-2, and 1 cell culture-adapted strain, EBCV-L9-80. Sequential cytopathic changes were microscopically monitored. Medium samples for titration of hemagglutinins and viral infectivity were collected directionally from both domains of the infected cell cultures at various intervals. RESULTS: Polarized epithelioid HRT-18G cells from apical domains had maximal susceptibility to infection with the EBCV and RBCV strains, and those from basolateral surfaces had minimal susceptibility. Titers of hemagglutinins and infective progeny BCV reached 1,280 hemagglutinin units and 4.2 x 10(8) plaque-forming units/ml for apical samples, but were minimal for basolateral samples. Asymmetric virus release occurred through the apical surfaces of the HRT-18G cells by 12 hours after infection when cell fusion as a sign of cytopathic changes began. When cells were infected basolaterally, progeny virions released from apical surfaces reinfected the target cells from the apical domains and induced cytopathic changes were delayed about 12 hours, compared with changes detectable in apically exposed cultures. CONCLUSIONS: EBCV and RBCV, isolated from cattle, had marked tropism for polarized epithelioid HRT-18G cells. Entry of BCV into the polarized HRT-18G cells was effected maximally through the apical domains and minimally through the basolateral domains. Release of progeny BCV occurred preferentially from the apical domains.