T cell responses in calves vaccinated with formalin-inactivated bovine respiratory syncytial virus (BRSV) prior to BRSV challenge

Respiratory syncytial virus (RSV) and bovine RSV (BRSV) are important causes of bronchiolitis and pneumonia in humans and cattle. Vaccine development for RSV/BRSV has been problematic; the landmark example was the occurrence of enhanced disease in children vaccinated with formalin-inactivated RSV (FI-RSV). Success of future vaccines depends on clarification of mechanisms of vaccine enhanced disease. In the work described, the immunopathogenesis of FI-RSV enhanced disease was studied in a bovine model. The second chapter details the experimental model. Calves were challenged once by aerosol exposure; clinical signs included fever, cough, dyspnea, and adventitious lung sounds. Necropsy revealed necrotizing proliferative bronchiolitis and alveolitis. The third chapter describes studies of T cell responses, clinical signs, and pathology in calves vaccinated with FI-BRSV prior to BRSV challenge. Interferon gamma (IFN-gamma) production and lymphocyte transformation (LT) by peripheral blood mononuclear cells (PBMC) stimulated with BRSV were measured. PBMC from FI-BRSV vaccinated (V/C) calves produced significantly less (IFN-gamma) than PBMC from mock vaccinated (M/C) calves postchallenge (PC). No significant LT responses to BRSV occurred. V/C calves had significantly higher clinical scores and significantly more severe alveolitis at postmortem than M/C calves. The fourth chapter describes postchallenge measurements of cytotoxic T lymphocyte (CTL) activity and the T cell cytokines (IFN-gamma) interleukin 2 (IL-2), and IL-4 in V/C and M/C calves. CTL activity of PBMC and of lymphocytes derived from a pulmonary lymphatic cannula (LDL) was measured. Cytokines were measured by semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) amplification of mRNA from LDL. CTL activity was not significantly different between V/C and (M/C) calves. LDL CTL activity and PBMC CTL activity were not significantly different. Message for all 3 cytokines was identified in both groups; there was no difference in amount of mRNA expressed or the pattern of expression. IL-2 was identified on all days PC. (IFN-gamma) was low to absent early and peaked on days 7--8. IL-4 was variably identified throughout infection. Clinical signs and pathology in both groups was diminished compared to earlier studies due to problems with the challenge isolate; this may have impacted CTL and RT-PCR studies. FI-BRSV vaccination of calves led to enhanced disease postchallenge. (IFN-gamma) production by PBMC was significantly decreased in V/C calves. In a subsequent study, CTL activity and levels of mRNA for (IFN-gamma) IL-2, and IL-4 were not significantly different in V/C versus M/C calves. The bovine model of RSV is a valuable resource for future studies of RSV pathogenesis and novel vaccines.