Abstract
The thymus is the main lymphoid organ that regulates the immune and endocrine systems by controlling thymic cell proliferation and differentiation. The gland is a primary lymphoid organ responsible for generating mature T cells into CD4+ or CD8+ single-positive (SP) T cells, contributing to cellular immunity. Regarding humoral immunity, the thymic plasma cells almost exclusively secrete IgG1 and IgG3, the two main complement-fixing effector IgG subclasses. Deformity in the thymus can lead to inflammatory diseases. Hassall’s corpuscles’ epithelial lining produces thymic stromal lymphopoietin, which induces differentiation of CDs thymocytes into regulatory T cells within the thymus medulla. Thymic B lymphocytes produce immunoglobulins and immunoregulating hormones, including thymosin. Modulation in T cell and naive T cells decrement due to thymus deformity induce alteration in the secretion of various inflammatory factors, resulting in multiple diseases. Influenza virus activates thymic CD4+ CD8+ thymocytes and a large amount of IFNγ. IFNs limit virus spread, enhance macrophages’ phagocytosis, and promote the natural killer cell restriction activity against infected cells. Th2 lymphocytes-produced cytokine IL-4 can bind to antiviral INFγ, decreasing the cell susceptibility and downregulating viral receptors. COVID-19 epitopes (S, M, and N proteins) with ≥90% identity to the SARS-CoV sequence have been predicted. These epitopes trigger immunity for antibodies production. Boosting the immune system by improving thymus function can be a therapeutic strategy for preventing virus-related diseases. This review aims to summarize the endocrine-immunoregulatory functions of the thymus and the underlying mechanisms in the prevention of COVID-19.
Highlights
The coronavirus family was first identified in the late [1]
The naive T lymphocytes disembark the thymus into the secondary lymphoid organs such as lymph nodes, where they are activated by foreign peptides of major histocompatibility complex (MHC) that are found on the surfaces of the antigen-presenting cells (APCs)
There is compelling evidence that the thymus is responsible for the development and differentiation of T lymphocytes
Summary
The coronavirus family was first identified in the late [1]. In the decades since, the world has experienced many lethal episodes of the coronavirus family. The naive T lymphocytes disembark the thymus into the secondary lymphoid organs such as lymph nodes, where they are activated by foreign peptides of MHC that are found on the surfaces of the antigen-presenting cells (APCs) This type of activation results in the proliferation and differentiation of effector T lymphocytes into four types that can produce cytokines and respond to different pathogens. The aim of the current study is to support the notion that a defect in thymic tolerogenic function is implicated as an essential factor in the pathophysiology of autoimmunity and virus-related diseases, including COVID-19 This piece of work underpins the reported literature on the physiology of the thymus (Figure 1) and the biological role of different thymic hormones with regard to the modulation of inflammatory responses and involvement in the maturation and differentiation of immune cells, as well as advocating the clinical and biological application in the treatment of inflammatory. Vaccines 2021, 9, x FOR PEER REVIEW of 19 disorders, including viral diseases
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