Infectivity-neutralizing and hemagglutinin-inhibiting antibody responses to respiratory coronavirus infections of cattle in pathogenesis of shipping fever pneumonia

Respiratory bovine coronaviruses (RBCV) emerged as an infectious agent most frequently isolated from respiratory tract samples of cattle with acute re spiratory tract diseases. Infectivity-neutralizing (IN) and hemagglutinin-i nhibiting (HAI) antibodies induced by RBCV infections were monitored in seq uential serum samples collected from cattle during a naturally evolving and experimentally monitored epizootic of shipping fever pneumonia (SFP), Catt le nasally shedding RBCV at the beginning of the epizootic started with low levels of serum IN and HAI antibodies. An increase in serum IN antibody af ter day 7 led to reduction of virus shedding in nasal secretions by the maj ority of the cattle between days 7 and 14. A substantial rise in the serum HAI antibody was observed during the initial phase among the sick but not t he clinically normal cattle which were infected with RBCV. The RBCV isolati on-positive cattle that developed fatal SFP had minimal serum IN and HAI an tibodies during the course of disease development. Cattle that remained neg ative in RBCV isolation tests entered this epizootic with high levels of se rum IN and HAI antibodies, which dramatically increased during the next two weeks. Protection against SFP was apparently associated,vith significantly higher levels of serum IN antibodies at the beginning of the epizootic. Th e RBCV-neutralizing activity is associated with serum immunoglobulin G (IgG ), particularly the IgG2 subclass, while RBCV-specific HAI antibody is rela ted to both serum IgG and IgM fractions.