Unilateral nasal infection of cotton rats with respiratory syncytial virus allows assessment of local and systemic immunity.

An in vivo model for the study of local and systemic effectors of immunity to respiratory syncytial virus (RSV) is described. Cotton rats (Sigmodon fulviventer) inoculated in one nostril with a small volume (2 microliters) of virus suspension contracted a unilateral nasal infection which did not extend to the contralateral nasal turbinates, nor to the lungs. Immunity to subsequent RSV challenge could be induced by small priming doses ( < 10 p.f.u. per animal), but was dependent upon viral replication, as virus inactivated by UV light was not immunogenic. Immunity occurred in the absence of detectable neutralizing serum antibody. The onset of resistance to viral challenge occurred simultaneously in ipsilateral nasal, contralateral nasal and pulmonary tissues. However, low levels of transient viral replication occurred in contralateral nasal turbinates and in lungs following virus challenge, thus indicating that local components of immunity acting at the ipsilateral site of infection were more effective than systemic components acting at the other sites. Further evidence is provided to suggest that three types of immunological effectors - local, persistent, systemic and transient systemic - participate in the immune response to RSV infection.