Lytic cell death mechanisms in human respiratory syncytial virus-infected macrophages

Abstract

Human respiratory syncytial virus (hRSV) is the most common cause of viral pneumonia in infants and children worldwide and creates significant airway disease in immunocompromised people and the elderly. Inflammation induced by hRSV infection is responsible for its hallmark manifestations of bronchiolitis and pneumonia. The cellular debris created secondary to lytic cell death of infected cells is a potent initiator of this inflammation. Macrophages are known to play a pivotal role in the early innate immune and inflammatory response to viral pathogens. While previous studies have investigated the mechanisms responsible for lytic cell death in Influenza A-infected macrophages and hRSV-infected neutrophils, the lytic cell death mechanisms associated with hRSV infection in macrophages remain unknown. In order to address this knowledge gap, we treated an hRSV-infected human THP-1 macrophage cell line with various inhibitors that block two lytic cell death pathways: pyroptosis and necroptosis. In addition, we used pyroptosis-deficient human macrophages to further clarify the lytic cell death mechanisms occurring during infection. Our studies revealed that hRSV induces lytic cell death in macrophages via both pyroptosis and necroptosis, specifically through caspase-1 and inflammasome-dependent pyroptotic mechanisms and through RIPK1-RIPK3-MLKL necroptotic mechanisms of cell death.