Formalin-inactivated bovine RSV vaccine enhances a Th2 mediated immune response in infected cattle

Safe RSV vaccine development has challenged the medical community since a formalin-killed RSV vaccine caused disease exacerbation in the 1960s. Disease was replicated using the bovine RSV system in one of two studies. The studies differed in viral protein dose and length of time between vaccination and infection. Disease exacerbation occurred in study 2 (previously reported). We hypothesized that low protein concentration in study 2's vaccine stimulated a TH2/IgE response that enhanced disease. BRSV-specific IgG1, IgG2, and IgE were measured by ELISA/Western blot from vaccinated/infected, vaccinated/mock infected, mock vaccinated/infected calves in both studies. Results revealed that study 2 calves produced more IgE, particularly to the nucleoprotein (N); IgE among study 2 calves correlated with high clinical scores. In contrast, study 1 calves showed stronger IgG responses to viral proteins.