背景:男女之间免疫反应的差异导致主要影响女性的自身免疫性疾病的发病率存在强烈的性别偏见,如多发性硬化症(MS)。MS的女性数量是女性的两倍多,使性行为成为最重要的危险因素之一。然而,尚不完全了解哪些基因导致自身免疫发病率的性别差异。为了解决这个问题,我们在女性和男性人类脾脏中进行了基因表达分析,并确定跨膜蛋白CD99是男性中最显著差异表达的基因之一。据报道,CD99参与免疫细胞迁移和T细胞调节,但性别特异性影响尚未得到全面调查。
方法:在本研究中,我们使用基因型-组织表达(GTEx)项目数据集在女性和男性人类脾脏中进行了基因表达分析,以鉴定女性和男性之间的差异表达基因.在人类免疫细胞亚群的蛋白质水平上成功验证后,我们评估了CD99的激素调节及其对原代人T细胞和JurkatT细胞中T细胞调节的影响。此外,我们在野生型小鼠和Cd99缺陷小鼠中进行了体内测定,以进一步分析差异CD99表达的功能后果.
结果:这里,我们发现,与女性相比,男性脾脏中CD99基因表达更高,并证实了T细胞和pDC表面蛋白质水平的这种表达差异。作为跨性别男性样品的体外测定和离体分析所显示的原因,雄激素可能是可有可无的。在脑脊液中,与血液相比,T细胞上的CD99更高。值得注意的是,男性MS患者CSF中CD4+T细胞的CD99水平较低,与控件不同。相比之下,两种性别在小鼠中的CD99表达相似,与野生型相比,Cd99缺陷小鼠对实验性自身免疫性脑脊髓炎的易感性相同.功能上,CD99在人T细胞活化后增加,并在阻断后抑制T细胞增殖。因此,CD99缺陷的JurkatT细胞显示细胞增殖和簇形成减少,通过CD99重新引入而获救。
结论:我们的结果表明,CD99在健康个体和MS患者中受到性别特异性调节,并且在人类中参与T细胞共刺激,而在小鼠中不参与。CD99可能以性别特异性方式导致MS发病率和易感性。
免疫系统保护我们免受细菌和病毒感染,并影响许多疾病的结果。因此,了解免疫过程对于解开致病机制和开发新的治疗方案至关重要。性别是影响免疫力的生物学变量,众所周知,女性和男性的免疫反应不同。与男性相比,女性会产生更强的免疫反应,从而更快地控制感染并提高疫苗效力。然而,这种增强的免疫反应伴随着女性对自身免疫性疾病如系统性红斑狼疮的优势和易感性,类风湿性关节炎和多发性硬化症(MS)。MS性别比例约为2:1至3:1,女性MS患者的发病率稳步上升,性别是发展MS的主要危险因素之一。然而,潜在的生物学机制,包括性激素,遗传和表观遗传因素及其复杂的相互作用仍然未知。这里,我们发现该基因及其编码蛋白CD99在女性和男性之间差异表达,男性在包括T细胞在内的许多免疫细胞亚群上表达增加。由于T细胞是MS发病机制的关键贡献者,我们研究了CD99对健康个体和MS患者T细胞的作用.我们能够鉴定CD99介导的T细胞调节,这可能导致MS易感性和发病率的性别差异,表明将性别作为生物学变量的重要性。值得注意的是,这些差异在小鼠中没有再现,这表明人类功能研究的必要性。
BACKGROUND: Differences in immune responses between women and men are leading to a strong sex bias in the incidence of autoimmune diseases that predominantly affect women, such as multiple sclerosis (MS). MS manifests in more than twice as many women, making sex one of the most important risk factor. However, it is incompletely understood which genes contribute to sex differences in autoimmune incidence. To address that, we conducted a gene expression analysis in female and male human spleen and identified the transmembrane protein CD99 as one of the most significantly differentially expressed genes with marked increase in men. CD99 has been reported to participate in immune cell transmigration and T cell regulation, but sex-specific implications have not been comprehensively investigated.
METHODS: In this study, we conducted a gene expression analysis in female and male human spleen using the Genotype-Tissue Expression (GTEx) project dataset to identify differentially expressed genes between women and men. After successful validation on protein level of human immune cell subsets, we assessed hormonal regulation of CD99 as well as its implication on T cell regulation in primary human T cells and Jurkat T cells. In addition, we performed in vivo assays in wildtype mice and in Cd99-deficient mice to further analyze functional consequences of differential CD99 expression.
RESULTS: Here, we found higher CD99 gene expression in male human spleens compared to females and confirmed this expression difference on protein level on the surface of T cells and pDCs. Androgens are likely dispensable as the cause shown by in vitro assays and ex vivo analysis of trans men samples. In cerebrospinal fluid, CD99 was higher on T cells compared to blood. Of note, male MS patients had lower CD99 levels on CD4+ T cells in the CSF, unlike controls. By contrast, both sexes had similar CD99 expression in mice and Cd99-deficient mice showed equal susceptibility to experimental autoimmune encephalomyelitis compared to wildtypes. Functionally, CD99 increased upon human T cell activation and inhibited T cell proliferation after blockade. Accordingly, CD99-deficient Jurkat T cells showed decreased cell proliferation and cluster formation, rescued by CD99 reintroduction.
CONCLUSIONS: Our results demonstrate that CD99 is sex-specifically regulated in healthy individuals and MS patients and that it is involved in T cell costimulation in humans but not in mice. CD99 could potentially contribute to MS incidence and susceptibility in a sex-specific manner.
The immune system protects us from bacterial and viral infections and impacts the outcome of many diseases. Thus, understanding immunological processes is crucial to unravel pathogenic mechanisms and to develop new therapeutic treatment options. Sex is a biological variable affecting immunity and it is known that females and males differ in their immunological responses. Women mount stronger immune responses leading to more rapid control of infections and greater vaccine efficacy compared to men. However, this enhanced immune responsiveness is accompanied by female preponderance and susceptibility to autoimmune diseases like systemic lupus erythematosus, rheumatoid arthritis and multiple sclerosis (MS). MS sex ratio varies around 2:1 to 3:1 with a steadily increasing incidence in female MS patients making sex one of the top risk factors for developing MS. However, the underlying biological mechanisms including sex hormones as well as genetic and epigenetic factors and their complex interplay remain largely unknown. Here, we discovered the gene and its encoded protein CD99 to be differentially expressed between women and men with men showing increased expression on many immune cell subsets including T cells. Since T cells are key contributors to MS pathogenesis, we examined the role of CD99 on T cells of healthy individuals and MS patients. We were able to identify CD99-mediated T cell regulation, which might contribute to sex differences in MS susceptibility and incidence indicating the importance to include sex as a biological variable. Of note, these differences were not reproduced in mice showing the necessity of functional research in humans.