Evidence of a cross-protective immune response to influenza A in the cotton rat model

Epidemiologic evidence suggests that cross-protective immune responses to influenza A viruses that have different hemagglutinin and neuraminidase subtypes occur in humans. This study characterized this heterosubtypic immunity in cotton rats (Sigmodon hispidus). Animals were infected with influenza A/PR/8/34 (H1N1) or A/Wuhan/359/95 (H3N2), and then challenged with A/Wuhan/359/95(H3N2) virus 4 weeks later. Viral titers, respiratory rates, and pathology of the respiratory tract following primary and secondary infection were compared. Cross-protection from heterosubtypic influenza A challenge in cotton rats was characterized by enhanced viral clearance, protection from tachypnea, a vigorous early cellular recall response, and a reduction in bronchiolar epithelial cell damage. Cross-protection was retained in steroid treated animals, in which the inflammatory recall response was minimal. Identification of the mechanisms that contribute to cross-protection in cotton rats may lead to the development of influenza vaccine strategies that are broadly protective.