Roles of Host Phospholipase D during Aspergillus fumigatus Infection in Mice

Abstract

Aspergillus fumigatus infection in the lungs is accompanied by the recruitment of innate immune cells, phagocytosis, and the release of inflammatory factors. Phospholipase D (PLD) is a key regulator of cell migration and phagocytosis, but the effect of PLD deficiency on antifungal infection in animals is unknown. This study aims to investigate the impact of PLD on the host immune response to A. fumigatus infection under either immunocompetent or immunosuppressed status. The invasive pulmonary aspergillosis mouse model was created using a modified protocol with immunosuppression by steroids. For collection of bronchoalveolar lavage fluid (BALF) from mice, the lungs were washed eight times with 0.5 ml of PBS. Total cell counts in BALF were determined using a Coulter Counter. The content of alveolar macrophages, neutrophils, and monocytes in BALF was examined by flow cytometry and analyzed by FlowJo V10 software. Multiplex immunoassays were used to determine the concentrations of inflammatory cytokines in BALF. In immunocompetent mice, alveolar macrophages were the major cell population in BALF after A. fumigatus infection, and a number of neutrophils and monocytes were recruited in the alveoli. Loss of both pld1 and pld2 genes did not affect the content of alveolar macrophages, neutrophils, or monocytes in BALF. Under immunosuppression induced by hydrocortisone acetate, pld1-/-pld2-/- mice showed higher mortality after A. fumigatus infection and had a higher fungal burden and much lower number of prominent focal areas of dense inflammatory infiltrates in lung tissue than wild type mice. Moreover, interleukin (IL)-12p40 significantly decreased, and IL-10 markedly increased, in BALF from pld1 -/- pld2 -/- mice after infection. Our findings revealed that, during A. fumigatus infection, deficiency in both pld1 and pld2 in mice was not conducive to the infiltration of inflammatory cells into lung tissue but promoted the release of IL-10 and blocked the release of IL-12, thereby increasing fungal burden and mortality.