Cytokine and Acute Phase Response in Calves Following Experimental Infection with BRSV

Bovine respiratory syncytial virus has been identified as an important pathogen associated with acute respiratory disease in calves. An infection model has been developed reflecting the clinical course and the development of pathological signs during a natural BRSV-infection. Calves were infected at age 15-20 weeks and reinfected 14 weeks later. Clinical signs and virus excretion were monitored daily. Blood samples were obtained in the whole period and investigated for the acute phase proteins: haptoglobin and serum amyloid A (SAA) and for the cytokines: interleukin-2 (IL-2), interleukin-4 (IL-4), interleukin-6 (IL-6) and interferon-gamma (IFN(). Haptoglobin and SAA were measured by ELISA and cytokine expression (mRNA) were determined by a quantitative real time RT-PCR (Taq-Man technology). The results showed an induction of IL-6, haptoglobin, SAA and IFNγ, to the first experimental infection, whereas there was a smaller induction of IFNγ, and no induction of IL-6, haptoglobin and SAA in the reinfection. Indication of a correlation was found between IL-6 expression and clinical signs and also acute phase protein induction and clinical signs. Another correlation was found between IFNγ and virus excretion. In conclusion, it seems that early mediators are important for the clinical outcome of infection, and that cytokines and acute phase proteins can be useful as clinical parameters reflecting the establishment, development and severity of the infection.