The immune response to human metapneumovirus is associated with aberrant immunity and impaired virus clearance in BALB/c mice.

Human metapneumovirus (HMPV), recently identified in isolates from children hospitalized with acute respiratory tract illness, is associated with clinical diagnosis of pneumonia, asthma exacerbation, and acute bronchiolitis in young children. HMPV has been shown to cocirculate with respiratory syncytial virus (RSV) and mediate clinical disease features similarly to RSV. Little is known regarding the pathophysiology or immune response associated with HMPV infection; thus, animal models are needed to better understand the mechanisms of immunity and disease pathogenesis associated with infection. In this study, we examine features of the innate and adaptive immune response to HMPV infection in a BALB/c mouse model. Primary HMPV infection elicits weak innate and aberrant adaptive immune responses characterized by induction of a Th2-type cytokine response at later stages of infection that coincides with increased interleukin-10 expression and persistent virus replication in the lung. Examination of the cytotoxic T lymphocyte and antibody response to HMPV infection revealed a delayed response, but passive transfer of HMPV-specific antibodies provided considerable protection. These features are consistent with virus persistence and indicate that the immune response to HMPV is unique compared to the immune response to RSV.