H. polygyrus monocytosis results in higher numbers of lung mononuclear phagocytes early after RSV infection.
RSV induced monocyte influx and subsequent accumulation of lung mononuclear phagocytes is crucial for the production of cytokines associated with the antiviral response13. To ascertain if this early influx was altered following H. polygyrusinfection, we used flow cytometry to assess the monocyte-macrophage compartment eight hours post RSV infection. RSV infection alone increased the numbers of mononuclear phagocytes in the lung (Fig. 5A), as others have observed, but after prior infection with H. polygyrus their counts were significantly higher than after RSV infection alone (Fig. 5B). This expansion was seen in both Ly6C+ and CD11c+ macrophages (Fig. 5C,D). Four days after RSV infection, numbers of Ly6C+macrophages remained higher in mice with prior H. polygyrusinfection, while the increase in numbers of CD11c+macrophages did not persist (Fig. 5E). Alveolar macrophage numbers were unaffected by prior H. polygyrus infection at both 8 and 96 hours post RSV infection (Fig. S1A,B). These findings demonstrate thatH. polygyrus infection leads to numbers of lung mononuclear phagocytes that exceed those found early after RSV infection alone, raising the possibility that high numbers of these cells confers an early protective effect against RSV infection.