Isotype-specific antibody responses of cattle to Salmonella Dublin lipopolysaccharide and porin following Salmonella Dublin vaccination and acute andchronic infection

Stimulation of different T-cell subsets during antigen presentation influen ces the antibody isotype response to an antigen. Salmonella infection and S almonella bacterin vaccination are likely to stimulate different T-cell sub types. The objective of this study was to determine whether there are diffe rences in the isotype response of cattle to Salmonella antigens following S almonella infection and Salmonella bacterin vaccination. Sera from Salmonel la bacterin-vaccinated, experimentally infected, and chronically infected ( carrier) adult cattle collected during previous studies was used to evaluat e the IgG(1), IgG(2), and IgM isotype responses of cows to Salmonella serot ype Dublin lipopolysaccharide (LPS) and porin. Following vaccination and ex perimental oral infection, IgG(1) titers to LPS and porin rose more quickly and persisted longer than did IgG(2) titers. In contrast to Salmonella inf ection, bacterin vaccination stimulated a weak response to Salmonella porin . Salmonella infection also induced a higher IgG(2):IgG(1) titer ratio to L PS than did bacterin vaccination. Chronic Salmonella infection induced the highest LPS and porin IgG(2):IgG(1) titer ratios and the highest correlatio n between LPS and porin titers. Response operating characteristic curves fo r each isotype-specific enzyme-linked immunosorbent assay (ELISA) were dete rmined to evaluate the effect of isotype on the sensitivity and specificity of Salmonella ELISA serology for distinguishing sera of Salmonella carrier s from those of vaccinated and acutely infected cows. IgG(2) titers to LPS and porin provide a more specific indicator of chronic Salmonella infection status than do IgG(1) titers to the same antigens with little to no loss i n sensitivity.