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Journal 'Cytokines & inflammation', 2003, No. 1

CYTOKINES IN THE THYMUS. PRODUCTION AND RECEPTION OF CYTOKINES

A.A. Yarilin

Thymic cells of the all types are able to produce cytokines - after a stimulation or spontaneously. The main cell producers of cytokine in the thymus are thymic epithelial cells (TEC) and thymocytes. Subcapsular and medullar TEC are more active cytokine producers than cortical TEC. The cytokine spectrum produced by TEC is similar to that produced by monocyte/macrophages. Cytokines are secreted also by other thymic non-lymphoid cells - fibroblasts, myoid, dendritic cells, macrophages. The ability of thymocytes to produce cytokines and express cytokine receptors is gradually reduced as they mature from the stage of CD44+CD3-CD4-CD8- precursor cells to the stage of CD3loCD4+CD8+ cortical thymocytes; on the latter stage both these capacities become completely blocked. After the completion of selection process the capacity of thymocytes to produce cytokines and respond to their action is restored. The nature of stimuli, which induce cytokine production in the thymus, is studied insufficiently. In experiments in vitro a cytokine production can be induced by TCR-CD3 binding or bypass activation. Intercellular contacts (particularly contacts between thymocytes and TEC) are important for induction and modulation of cytokine secretion. Peptide hormones and cytokines themselves regulate cytokine production. Thus, "the minor cytokine network" exists in the thymus. An expression of cytokine receptors is studied mainly for thymocytes. A receptor expression corresponds to needs in the respective cytokine action. Thus, IL-7 receptor is expressed on the stages of double-negative and single-positive thymocytes, which are the main consumer of IL-7. Expression of chemokine receptors and localization of respective chemokines production in concert determine the direction of migration, which these cells will have to realize.

Keywords: thymic epithelial cells, thymocytes, TCR, peptide hormones, cytokines, chemokines, cytokine receptors.

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