IRF5 as a potential immunological biomarker in lung adenocarcinoma.

Background: In the clinic, the primary conventional treatments of advanced non-small cell lung cancer (NSCLC) are surgery, radiation therapy, and chemotherapy. In recent years, immune checkpoint inhibitors (ICIs) have shown promise in optimizing therapeutic benefits when combined with other immunotherapies or standard therapies. However, effective biomarkers for distant metastasis or recurrence have yet to be identified, making it difficult to determine the best therapeutic approaches. The effect of tumor immunotherapy, as well as metastasis and recurrence, are thought to be significantly affected by the tumor immunosuppressive microenvironment. Transcription factor interferon regulatory factor 5 (IRF5) is a critical regulator of the immune response. It has been found to play an important role in malignant tumor transformation, immune regulation, clinical prognosis, and the treatment response. Nevertheless, its precise role in the advancement of NSCLC, including lung adenocarcinoma (LUAD) remains poorly understood. This study sought to investigate the expression of IRF5 in LUAD and its effect on patient prognosis, and examine the biological function of IRF5. Additionally, the study aimed to examine the association between IRF5 expression and immune cell infiltration, as well as its correlation with key immune checkpoint genes relevant to NSCLC. Methods: LUAD RNA-sequencing data and clinical information were downloaded from The Cancer Genome Atlas (TCGA) and analyzed. A tissue microarray (TMA) analysis was conducted to detect IRF5 expression, and immunofluorescence staining was performed to determine immune infiltration. Bioinformatics and TMA analyses, including a differential expression analysis, prognosis prediction analysis, correlation analysis, immune infiltration analysis, and gene set enrichment analysis (GSEA), were conducted using the TCGA dataset. Results: The results showed that the expression levels of IRF5 were lower in the LUAD tissues than the normal lung tissues. Patients with high IRF5 expression had longer survival times than those with low IRF5 expression. IRF5 was also found to be correlated with lymph node metastasis. Nine distinct types of immune cells were identified between the groups with high and low IRF5 expression levels. Eight major immune checkpoint genes were found to be upregulated in LUAD patients with high IRF5 expression levels. The enrichment analyses showed that various immune pathways were enriched in the LUAD samples with IRF5, including T cell activation, lymphocyte activation, and T cell receptor activation. Conclusions: IRF5 expression is closely related to tumor immunity and immunotherapy in LUAD patients. IRF5 may be indicative of prognosis in LUAD patients.