The role of macrophage phagocytosis on respiratory pneumovirus infection and host defense

Lung macrophages play a pivotal role in the defense against viral and bacterial infections. These specialized cells are equipped with multiple mechanisms, such as phagocytosis, to detect the presence of pathogens and clear the infections. Human Metapneumovirus (HMPV) is a leading cause of acute lung infection, affecting particularly young children and the elderly. During and after the HMPV infection, individuals are at an increased risk of secondary bacterial infections due to a decreased immune response capacity, which increases the severity of the disease. However, the cellular contribution of macrophages in the HMPV infection remains understudied. In this work, we investigated the role of macrophage phagocytosis in HMPV infection and the effect of HMPV on macrophage phagocytic activity. For that, we used THP-1- and PBMC-derived macrophages as experimental models. We found that macrophages were susceptible to HMPV infection and that phagocytosis is one of the mechanisms used by the virus to infect the cells. However, macrophages do not replicate the virus efficiently. Furthermore, viral infection decreases the capacity of macrophages to phagocyte bacteria, as demonstrated by the activity of intracellular pH indicator dye. These data highlight the importance of phagocytosis as a mechanism to control respiratory viral infections and the subversion of the host immunity by HMPV that may contribute to subsequent opportunistic bacterial infections.