AS a disease with a higher proportion of males, there are obvious differences in the clinical manifestations between male AS patients and female AS patients. Grubisi F et al.  indicated that the distribution of the clinical manifestations and specific radiological characteristics of AS in the sacroiliac joint and axial bone was gender-dependent, and that males were regarded as one of the risk factors associated with poor prognosis of AS. Jung YO et al.  found that males were younger at the onset of symptoms, had a higher positive rate of HLA-B27, and had a greater degree of involvement of the spinal cord on imaging. And females have less spinal involvement and better mobility, but a higher incidence of plantar fasciitis. Jimenez-balderas FJ et al.  suggested that male patients were more common in uveitis, bamboo spine and hip arthroplasty. And Calin A et al.  found that female patients with AS had A longer delay in diagnosis, which may miss the optimal treatment time. As, rheumatoid arthritis and systemic lupus erythematosus are all considered as autoimmune diseases. However, Rheumatoid arthritis and systemic lupus erythematosus are more common in females [34, 35]. The latter two are considered to have distinct sexual dimorphism in the immune mechanism [34, 36, 37, 38]. Some researches suggested that estrogen plays an important role in the immune mechanisms of these diseases [39, 40, 41]. However, AS usually occurs in males [1, 2]. Some researches have shown that the role of sex hormones in AS is not prominent, they can not directly explain the dominant position of male, nor directly explain its sexual characteristics [20, 21, 22, 42].
Due to the gender differences in clinical manifestations of AS, as well as gender differences in the composition and content of blood, we divided the samples into males and females. The Bioinformatics analysis of DEGs (M-AS vs M-NAS group, F-AS vs F-NAS group) was carried out respectively, and it was found that there were differences in GO function and KEGG pathways between the two groups. In terms of GO function, both male and female DEGs were mainly concentrated in biological processes. The difference is that the male DEGs mainly concentrated in natural killer cell mediated immunity, regulation of heart growth, etc. And female DEGs mainly concentrated in regulation of T cell receptor signaling pathway, regulation of CD4-positive, homeostasis of number of cells, etc. On the KEGG pathway, the male DEGs mainly concentrated in the Th1 and Th2 cell differentiation, Complement and coagulation cascades, etc. Female DEGs mainly concentrated in Th1 and Th2 cell differentiation, Human T-cell leukemia virus 1 infection, etc. It was found from the correlation network between hub-module-pathway genes and KEGG pathways that the most likely key genes for males were IL2RB, and the pathway were Th1 and Th2 cell differentiation, while the most likely key genes for females were CD3D, IL2RB and STAT5B, and the pathway were Th1 and Th2 cell differentiation. The expression of these key genes was further verified by QPCR and ELISA.
IL2RB protein binds with interleukin-2 in an intermediate or high affinity manner and participates in T-cell-mediated immune response [43, 44, 45]. Abnormalities of IL2RB can induce immune dysregulation driven by T and NK cells, leading to autoimmune diseases and immunodeficiency diseases . IL2RB is associated with a variety of immune diseases, such as inflammatory bowel disease, rheumatoid arthritis, multiple sclerosis, etc [47, 48, 49]. Polo Y La Borda J et al.  found that IL2RB was a participant in the development of peripheral arthritis of AS.
CD3D proteins are part of the T cell receptor/CD3 complex (TCR/CD3 complex) and participate in T cell development and signal transduction [51, 52]. TCR is responsible for identifying antigens associated with major histocompatibility complex (MHC) and initiating the cellular immune response [53, 54]. Doucey MA et al.  indicated that the coupling of CD3D and TCR is necessary for the effective activation and positive selection of CD8T cells. And activated CD8T cells were involved in the induction and maintenance of AS [55, 56].
Th1 and Th2 cell differentiation is the main pathogenesis of AS. There is only one key gene involved in this pathway in men, while there are two key genes involved in this pathway in women. This indicates that high expression of IL2RB may induce AS in men. The abnormalities of both IL2RB and CD3D may cause women to carry AS. Therefore, men are more likely to suffer from AS than women. This explains why the main population of AS patients is male. Both IL2RB and CD3D are immune-related genes, which further confirms that AS is an immune disease.