Antibody responses of cattle with respiratory coronavirus infections during pathogenesis of shipping fever pneumonia are lower with antigens of enteric strains than with those of a respiratory strain.

The serum antibody responses of cattle with respiratory coronavirus infections during the pathogenesis of shipping fever pneumonia were analyzed with different bovine coronavirus antigens, including those from a wild-type respiratory bovine coronavirus (RBCV) strain (97TXSF-Lu 15-2) directly isolated from lung tissue from a fatally infected bovine, a wild-type enteropathogenic bovine coronavirus (EBCV) strain (Ly 138-3), and the highly cell culture-adapted, enteric prototype strain (EBCV L9-81). Infectivity-neutralizing (IN) and hemagglutinin-inhibiting (HAI) activities were tested. Sequential serum samples, collected during the onset of the respiratory coronavirus infection and at weekly intervals for 5 weeks thereafter, had significantly higher IN and HAI titers for antigens of RBCV strain 97TXSF-Lu15-2 than for the wild-type and the highly cell culture-adapted EBCV strains, with P values ranging from <0.0001 to 0.0483. The IN and HAI antibody responses against the two EBCV strains did not differ significantly, but the lowest titers were detected with EBCV strain L9-81. The role of coronaviruses as respiratory pathogens in cattle was recently recognized when numerous coronavirus strains were isolated from the nasal secretions and lung tissues from cattle with fatal cases of shipping fever pneumonia (SFP). These isolates are referred to as respiratory bovine coronaviruses (RBCV) (18, 19). The enteropathogenic potential of coronaviruses was identified previously when these viruses were isolated from diarrhea fluid or intestinal samples from neonatal calves with severe diarrhea (7, 13). In addition, coronaviruses were implicated in winter dysentery of adult cattle (14). These coronaviruses are referred to as enteropathogenic bovine coronaviruses (EBCV). Significant phenotypic, antigenic, and genetic differences separate the newly recognized RBCV from EBCV (2, 3, 11, 18). Furthermore, infectivityneutralizing (IN) monoclonal antibodies (MAb) distinguished between the EBCV wild-type strain LY138-3 and the highly cell culture-adapted EBCV strain L9-81, as well as the Norden vaccine strain (8). Bovine coronaviruses are enveloped, have a positive singlestranded RNA genome of about 31 kb, and belong to the Coronaviridae family of the order Nidovirales (6). The spike (S) and the hemagglutinin esterase (HE) glycoproteins of the five structural proteins function in the infectious process through adsorption and coadsorption to the receptors on susceptible host cells (5, 6). The S and HE glycoproteins are both capable of hemagglutinating rodent and chicken red blood cells (RBC). The HE but not S glycoprotein facilitates the release of viruses adsorbed to RBC in the receptor-destroying enzyme (RDE) test mediated by an acetylesterase (AE) component of the HE (15–17, 20, 21). These two glycoproteins induce IN and hemagglutinin-inhibiting (HAI) antibodies. The objectives of the present investigations were to assess the antibody responses of cattle during a naturally occurring and experimentally monitored infection that had induced severe pneumonic signs, including SFP. The kinetics of IN and HAI antibody responses of these cattle were analyzed with antigens of an endogenous RBCV strain, which were isolated from lung tissue from a fatally infected bovine from this SFP epizootic, and with antigens of the wild-type and the highly cell culture-adapted EBCV strains. The analysis was conducted with sera sequentially collected from cattle which had primary and secondary immune responses to the RBCV infection.