An altered natural killer cell immunophenotype characterizes clinically severe pediatric RSV infection.

Respiratory syncytial virus (RSV) infects nearly all children by 2 years of age and is a leading cause of pediatric hospitalizations. A subset of children with RSV infection (RSV children) develop respiratory failure requiring intensive care, but immune mechanisms distinguishing severe pediatric RSV infection are not fully elucidated. Natural killer (NK) cells are key innate immune effectors of viral host defense. In this study of 47 critically ill RSV children, we coupled NK cell immunophenotype and cytotoxic function with clinical parameters to identify an NK cell immune signature of severe pediatric RSV disease. Airway NK cells were increased in intubated RSV children with severe hypoxemia and prolonged duration of mechanical ventilation and were correlated with clinical severity scores. Peripheral blood NK cells were decreased in RSV patients and had altered activating receptor expression, with increased expression of CD69 and decreased expression of NKG2D. Ex vivo, circulating NK cells from RSV patients exhibited functional impairment characterized by decreased cytotoxicity as well as aberrant immune synapse assembly and lytic granule trafficking. NK cell frequency and phenotype correlated with clinical measures that defined disease severity. These findings implicate a role for NK cells in mediating RSV immunopathology and suggest that an altered NK cell immunophenotype is associated with severe RSV disease in young children.