It has been proven that CD27 is involved in various types of tumors, such as breast cancer (20–23), lung cancer(24–26), gastric cancer(27–29), colon cancer(30, 31) ,liver cancer(32) and esophagus cancer(33). CD27 is closely associated with the tumor immune microenvironment. Studies have shown that high expression of CD27 promotes immune cells infiltration and enhances the efficacy of immune therapy (34–36). However, there is limited research on the role of CD27 in non-tumor diseases, such as HT. While the precise underlying causes of HT remain incompletely understood, it is widely acknowledged that immune responses play a pivotal role in the disease's development(15). Consequently, conducting a more comprehensive investigation into the immune aspects of HT holds significant promise for enhancing our understanding of its pathogenesis and improving treatment strategies.
In our study, we identified DEGs between normal and HT groups. Our GO enrichment analysis unveiled that these DEGs within the HT group were primarily implicated in processes such as lymphocyte differentiation, mononuclear cell differentiation, and the activation of immune responses. Additionally, our KEGG pathway analysis underscored strong associations between the DEGs in the HT group and critical pathways including the NOD-like receptor signaling pathway, T cell receptor signaling pathway, and Primary immunodeficiency. Furthermore, DO enrichment analysis shed light on the connection between the DEGs in the HT group and various immunological diseases, encompassing primary immunodeficiency disease, human immunodeficiency virus infectious disease, and Graves' disease. These findings underscore a substantial link between the pathogenesis of HT and immune system dysregulation, suggesting that immunotherapy could present novel therapeutic avenues for the clinical management of HT(37).
Subsequently, we employed WGCNA to pinpoint gene modules that exhibited a positive correlation with HT. Our WGCNA results unveiled two modules, namely module_turquoise and module_salmon, which displayed notably strong positive associations with HT, featuring correlation coefficients of 0.69 and 0.7, respectively. Within these modules, we identified 107 common genes shared with the DEGs for further exploration. To identify central genes within these modules, we constructed a protein-protein interaction network, ultimately identifying the top 10 hub genes, namely PTPRC, CD4, CD2, CD27, CD48, CD69, CD3E, CD5, CD3D, and CD53. Subsequently, we scrutinized the expression profiles of these genes in both the training and test groups. Our findings consistently revealed that these genes, particularly CD27, exhibited significantly elevated expression levels in the HT groups when compared to the control group, a pattern observed in both the training and test groups. Diagnostic ROC curves analysis revealed that these genes had good diagnostic value for HT in training group and test group. The cut off values of CD27 were 7.171and 7.012 in training groups and test groups. And the area under the ROC curves of CD27 was reached to 1 in training groups and test groups, respectively. The analysis of the nomograms indicated that the high expression of CD27 played an considerable role in the diagnosis of HT. The above results suggested that CD27 is upregulated in HT and plays nonnegligible role in the diagnosis of HT.
To gain further insights into the role of CD27 in HT and to elucidate its potential mechanisms, we stratified the HT samples in the training group into CD27-high and CD27-low groups, based on the median CD27 expression value. We then conducted a differential gene expression analysis within these two groups. The GO results highlighted that the DEGs were predominantly associated with the proliferation and differentiation of immune cells. These processes encompassed lymphocyte differentiation, mononuclear cell differentiation, B cell differentiation, lymphocyte proliferation, B cell activation, and mononuclear cell proliferation. In terms of pathways, the KEGG analysis revealed that the DEGs were primarily implicated in critical pathways such as the T cell receptor signaling pathway, PD-L1 expression and PD-1 checkpoint pathway in cancer, Primary immunodeficiency, Th17 cell differentiation, Cytokine-cytokine receptor interaction, and NOD-like receptor signaling pathway. Moreover, the GSEA results shed light on a positive correlation between CD27 expression and essential processes, including cytokine-cytokine receptor interaction, natural killer cell-mediated cytotoxicity, and the T cell receptor signaling pathway. These findings collectively indicate that CD27 plays a pivotal role in the development of HT, primarily by exerting regulatory control over the functioning of immune cells, with a particular emphasis on B cells and T cells.
The thyroid peroxidase antibodies synthesis in tissues or serum of patients with HT is causally related to immune cells infiltration. Consequently, we embarked on an analysis to explore the interplay between the levels of immune cell infiltration in the HT samples from the training group and CD27. The observation presented that CD27 is associated with a variety of immune cells and CD27 has a good correlation with T cells, and the correlation coefficient is 0.69. Above results hinted that eliminating immune cell infiltration in thyroid tissue may have a beneficial effect in curing HT.
More importantly, we observed the levels of CD27 mRNA and protein in clinical samples respectively, and the results showed that CD27 presented a high expression level in HT samples, which was consistent with the results obtained using public databases above. In addition, the expression levels of CD27 in thyroid cancer were also observed, and the results exhibited that CD27 mRNA level in malignancy groups turned out to be lower than normal groups and there was no difference in the protein level of CD27 in thyroid cancer as compared to the normal group. This further indicated that CD27 could distinguish between HT and thyroid cancer in diagnosis.