In this review, we described the structure and organization of antigen-recognizing repertoires of B and T cells from the standpoint of modern immunology. We summarized the latest advances in bioinformatics analysis of sequencing data from T and B cell repertoires and also presented contemporary ideas about the mechanisms of clonal diversity formation at different stages of organism development. At the same time, we focused on the importance of the allelic variants of the HLA genes and spectra of presented antigens for the formation of T-cell receptors (TCR) landscapes. The main idea of this review is that immune equilibrium and proper functioning of immunity are highly dependent on the interaction between the recognition and the presentation landscapes of antigens. Certain changes in these landscapes can occur during life, which can affect the protective function of adaptive immunity. We described some mechanisms associated with these changes, for example, the conversion of effector cells into regulatory cells and vice versa due to the trans-differentiation or bystander effect, changes in the clonal organization of the general TCR repertoire due to homeostatic proliferation or aging, and the background for the altered presentation of some antigens due to SNP mutations of MHC, or the alteration of the presenting antigens due to post-translational modifications. The authors suggest that such alterations can lead to an increase in the risk of the development of oncological and autoimmune diseases and influence the sensitivity of the organism to different infectious agents.
Aim. The aim of this study was the investigation of the influence of humoral factors of homeostatic proliferation IL-7 and IL-15 on T-regulatory cells in healthy donors.Materials and methods. The study included 15 conditionally healthy donors. Phenotyping and evaluation of expression changes of transcription factor FoxP3 and the main functional molecules on T-regulatory cells such as PD-L1, CTLA-4 and HLA-DR during cultivation under IL-7, IL-15 and anti-CD3 stimulation combined with IL-2 were performed by flow cytometry. Also, we estimated proliferation intensity of T-regulatory cells in the course of cultivation.Results. We revealed that humoral factors of homeostatic proliferation can effectively support a pool of T-regulatory cells during cultivation by number and phenotype and can maintain expression of important molecules such as PD-L1 and HLA-DR on regulatory T-cell surface. In addition, our study showed that IL-7 and IL-15 can cause relatively low T-regulatory cells proliferation in comparison to CD4+- lymphocytes.Conclusion. The observed ability of homeostatic proliferation factors to maintain T-regulatory cells pool presumably can play an important role in lymphopenic conditions when the number of effector cells is decreased and the insufficiency of interleukin IL-2 is observed, which plays a primary role in the homeostasis of T-regulatory cells in normal conditions.
It is well known that the most important feature of adaptive immunity is the specificity that provides highly precise recognition of the self, altered-self, and non-self. Due to the high specificity of antigen recognition, the adaptive immune system participates in the maintenance of genetic homeostasis, supports multicellularity, and protects an organism from different pathogens at a qualitatively different level than innate immunity. This seemingly simple property is based on millions of years of evolution that led to the formation of diversification mechanisms of antigen-recognizing receptors and later to the emergence of a system of presentation of the self and non-self antigens. The latter could have a crucial significance because the presentation of nearly complete diversity of auto-antigens in the thymus allows for the “calibration” of the forming repertoires of T-cells for the recognition of self, altered-self, and non-self antigens that are presented on the periphery. The central role in this process belongs to promiscuous gene expression by the thymic epithelial cells that express nearly the whole spectrum of proteins encoded in the genome, meanwhile maintaining their cellular identity. This complex mechanism requires strict control that is executed by several transcription factors. One of the most important of them is AIRE. This noncanonical transcription factor not only regulates the processes of differentiation and expression of peripheral tissue-specific antigens in the thymic medullar epithelial cells but also controls intercellular interactions in the thymus. Besides, it participates in an increase in the diversity and transfer of presented antigens and thus influences the formation of repertoires of maturing thymocytes. Due to these complex effects, AIRE is also called a transcriptional regulator. In this review, we briefly described the history of AIRE discovery, its structure, functions, and role in the formation of antigen-recognizing receptor repertoires, along with other transcription factors. We focused on the phylogenetic prerequisites for the development of modern adaptive immunity and emphasized the importance of the antigen presentation system.
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