Previous studies reported that age and sex had an opposite influence on the biological behavior of tumor pathogenesis, LNM, and long-term survival time of PTC (Rahbari, et al. 2010; Suteau, et al. 2021). Some studies speculated that this contradictory behavior originated from the difference in hormone levels and immune status in different sexes and ages. In women, the levels of estrogen and its receptor reached a peak value in reproductive age and then decreased with the advent of menopause (Caini, et al. 2015; Liu, et al. 2014; Rubio, et al. 2018). Moreover, estrogen and its receptors play an important role in autoimmune diseases, including Hashimoto's thyroiditis, which frequently occurs in women, especially in childbearing age (Doukas, et al. 2013; Khan and Ahmed 2016; Moulton 2018). Some studies found that Hashimoto's thyroiditis was a risk factor for PTC (Antonelli, et al. 2015; Noureldine and Tufano 2015). However, our previous study found that Hashimoto's thyroiditis was a protective factor for LNM in young groups (Yan, et al. 2022), which has been confirmed in several other studies (Kim, et al. 2011; Wang, et al. 2022). Some studies found that PTC with Hashimoto's thyroiditis as a background had a better prognosis (Lun, et al. 2013). Immune cell infiltration, including T and B cells, is an important component of autoimmunity. The changes in the immune microenvironment cause tumor pathogenesis, and the metastasis of lymph nodes varies in different sexes and ages.
In our study, LNM was more likely to occur in male and younger patients, which was consistent with other studies (Hu, et al. 2022; Tan, et al. 2022). In addition, we found TCL1A and CR2 with contrary trends between normal and tumor tissues and LNM, which might explain the reason why the biological behavior of thyroid tumors was contradictory in different ages and sexes. The scRNA-seq analysis showed that TCL1A and CR2 were mainly expressed in B lymphocytes and differed in different tissues, which strengthened the evidence of the influence of immunity on thyroid cancer. B cells play an important role in autoimmune diseases, not only by producing antibodies to participate in autoimmune reactions but also by secreting cytokines and chemokines to recruit T cells (Luu, et al. 2014). In addition, some marker proteins were expressed during the maturation of B cells, and were used to identify different subtypes; the dysfunction of B cells led to changes in autoimmune tolerance (Jiang, et al. 2020; Kang, et al. 2021).
TCL1A is a proto-oncogene, physiologically, which is only expressed in embryonic tissues and pre-mature B cells or early-T cells (Teitell 2005), and is overexpressed in some T cell or B cell lymphomas and epithelial solid tumors (Stachelscheid, et al. 2021). Some studies pointed out that TCL1A participated in the NANOG–TCL1A–Akt pathway (Lee, et al. 2015; Noh, et al. 2012; Song, et al. 2020), leading to epithelial–mesenchymal transition, tumor proliferation, and immune escape. The high expression of TCL1A was related to the LNM in breast cancer and the poorer prognosis in colon cancer (Li, et al. 2017; Srour, et al. 2020). However, a study on cervical cancer showed that the high expression of TCL1A in B cells was associated with an improved survival time (Punt, et al. 2015). Our study found that the infiltration of B cells related to TCL1A expression was significantly higher in para-tumor tissues and tissues with LNM than in corresponding tumor tissues and tissues without LNM. Previous studies found that the expression of TCL1A was downregulated during the maturation process and silenced in terminally differentiated B cells (Stachelscheid, et al. 2021). On the contrary, TCL1A participated in the conversion of T and B lymphocytes by changing the expression of proinflammatory cytokines and chemokines, which promoted the development of autoimmune diseases (Ho, et al. 2017). Also, the expression of TCL1A in lymphocytes was induced by estrogen, which depended on single-nucleotide polymorphism (Ho, et al. 2016). The regulation and imbalance of TCL1A were modified by various transcription and translation processes.
CR2 is a transmembrane glycoprotein expressed by mature B cells and dendritic follicular cells (Hannan 2016). It acts as a complement receptor to bind C3d and cooperate with BCR and then participates in complement-induced immune response (Bower and Ross 2006). In mice, the expression of CR2 lowers the activation threshold of B cells and significantly enhances the humoral immune response (Carroll and Isenman 2012). In human beings, the binding of BCR and CR2 is dose dependent and inhibits the activation of B cells under a weak stimulation of BCR (Kovacs, et al. 2021). In addition, CR2 regulates the tolerance of B cells and participates in autoimmunity. The expression of CR2 is reduced in patients with rheumatoid arthritis and systemic lupus erythematosus compared with healthy individuals (Asokan, et al. 2013; Asokan, et al. 2006; Prokopec, et al. 2010). In tumor immunity, CR2 can combine with the Fc receptor to assist in receptor-mediated tumor killing (Imai, et al. 2007).
Our study found that young and female patients had more TCL1A- and CR2-related B cell infiltration in para-tumor tissues and tissues with LNM than in tumor and nonmetastatic tissues. We explored whether LNM activates the tumor immune system by recruiting more lymphocytes. The influence of immune factors on the biological behavior of thyroid cancer has been confirmed, but the mechanism and pathway are complex and vague. Some studies on the single-cell RNA sequencing of thyroid cancer found different patterns of immune infiltration in thyroid cancer (Pan, et al. 2021), which affected the pathogenesis and metastasis of thyroid cancer. In addition, our study found a different proportion of CD3 + / CD8 + lymphocytes in peripheral blood with different lymph node states, which may help to evaluate the lymph node metastasis status before surgery. Our study supplemented this view on the dynamic changes in age and sex, and provided a direction for the natural evolution of thyroid cancer.
Our findings might help understand the role of sex and age in tumor pathogenesis and LNM of PTC, which is related to the expression of TCL1A and CR2 in B cells. The results enriched our knowledge of immune factors in PTC. However, our study was a single-center study, and hence the findings require further validation. Also, our study was conducted only on the transcription level. Hence, further proteomics research may help in obtaining more realistic results.