The production mechanism and immunosuppression effect of pulmonary surfactant protein D via toll like receptor 4 signaling pathway in human corneal epithelial cells during Aspergillus fumigatus infection

•SP-D can be stimulated by TLR4 during A. fumigatus infection in HCECs.•Recombinant human SP-D can inhibit the expression of inflammatory cytokines.•The immunosuppression function of SP-D may act through TLR4 signaling pathway.

ObjectiveTo observe the production mechanism of surfactant protein D (SP-D) in human corneal epithelial cells (HCECs) when infected by Aspergillus fumigatus (A. fumigatus) hyphae, and explore whether SP-D can inhibit the cell activations through toll-like receptor 4 signaling pathway during fungal infection.MethodsmRNA and protein expressions of SP-D were evaluated in HCECs after stimulation by A. fumigatus, with or without pretreatment of TLR4 inhibitor (CLI-095) by real time PCR and Western blot. The expression levels of inflammatory cytokines IL-1β and IL-8 evaluated when pretreated with SP-D antibody or recombinant human SP-D in fungi-stimulated HCECs by real time PCR and ELISA, IL-1β and IL-8 expressions were also detected in A. fumigatus-stimulated HCECs that pretreated with CLI095 or MyD88 inhibitor (Pepinh-MYD) and recombinant human SP-D.ResultsmRNA and protein levels of SP-D increased after stimulation of A. fumigatus for 16 h and 20 h respectively. The upregulation of SP-D could be inhibited by CLI-095. mRNA and protein expressions of IL-1β and IL-8 decreased significantly when pretreated HCECs with recombinant human SP-D for 4 h before A. fumigatus stimulation, while IL-1β and IL-8 increased when pretreated with SP-D antibody for 1 h. Pretreatment of CLI095 or Pepinh-MYD can increase the expressions of IL-1β and IL-8 mRNA and protein in HCECs induced by recombinant human SP-D and A. fumigatus.ConclusionsSP-D can be stimulated by TLR4 during A. fumigatus infection. Recombinant human SP-D can inhibit the expression of inflammatory cytokines through TLR4 signaling pathway.