Aspergillus fumigatus enhances human NK cell activity by regulating M1 macrophage polarization

The progression of disease caused by fungal infection is closely associated with the human immune system. Macrophages and natural killer cells (NK cells) are two important types of innate immune cells that serve an important role in anti‑infection immunity. There has been limited research into the interactions between fungi and macrophages. In the present in vitro study, reverse transcription‑quantitative PCR, ELISA and flow cytometry were performed to reveal that the interaction between macrophages and NK cells, regulated by Aspergillus fumigatus conidia, induced macrophages to polarize into M1 macrophages by secreting large quantities of tumor necrosis factor‑α, interleukin‑18 and Galectin‑9. In addition, when NK cells were co‑cultured with the conidia of A. fumigatus‑stimulated M1 macrophages, they exhibited increased activation levels and secretion of interferon‑γ (IFN‑γ). It was further demonstrated via antibody neutralization and gene silencing experiments that galectin‑9 served an important role in the interaction between macrophages and NK cells regulated by A. fumigatus. In conclusion, it was demonstrated that A. fumigatus induced the polarization of macrophages into M1 macrophages by secreting Galectin‑9, which then promoted NK cell activity and IFN‑γ secretion. The results provided improved understanding of the role of innate immune cells in invasive fungal infections. The present study also provided novel insight into the study of macrophages and NK cells in inflammatory infections caused by A. fumigatus and potential strategies to control the progression of inflammation.