Background: The programmed cell death 1 (PD-1)/PD-1 ligand 1 (PD-L1) signaling pathway is significantly upregulated in severe influenza virus infection, which impairs the immune system and causes increased tissue inflammation and damage. Blocking this signaling pathway will reduce the damage, lower the virus titer in lung tissue, and alleviate the symptoms of infection to promote recovery. The aim of this study was to identify the key factors and regulatory mechanisms in the PD-1 checkpoint blockade–responsive immune microenvironment in severe influenza infection.
Methods: A BALB/c mouse model of severe influenza A/H1N1 infection was constructed, and whole-transcriptome sequencing of mice treated with PD-1 checkpoint blockade before severe A/PR8(H1N1) influenza infection and IgG2a isotype control before infection were performed. Subsequently, the differential expression of nucleic acids between these two groups was analyzed, followed by functional interaction prediction analysis to investigate gene-regulatory circuits.
Results: In total, 84 differentially expressed (dif) mRNAs, 36 dif-microRNAs (miRNAs), 90 dif‑lncRNAs (long noncoding RNAs), and 22 dif-circRNAs (circular RNAs) were found in PD-1 antagonist treated A/PR8(H1N1) influenza infection lung compared with the controls (IgG2a isotype control treated before infection). In spleens between the above two groups, 45 dif-mRNAs, 36 dif-miRNAs, 57 dif-lncRNAs, and 24 dif-circRNAs were identified. Direct function enrichment analysis of dif-mRNAs and dif-miRNAs showed that these genes were mainly involved in myocardial damage related to viral infection, mitogen activated protein kinase (MAPK) signaling pathways, RAP1 (Ras-related protein 1) signaling pathway, and Axon guidance. Finally, 595 interaction pairs were obtained for the lungs and 462 interaction pairs for the spleen were obtained in the competing endogenous RNA (ceRNA) complex network, in which the downregulated mmu‑miR-7043-3p and Vps39-204 were enriched significantly.
Conclusions: The present study provided a basis for the identification of potential pathways and hub genes that might be involved in the PD-1 checkpoint blockade–responsive immune microenvironment in severe influenza infection.