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IL-7 is a key factor for the survival and maintenance of CD4+ central (Tcm) and effector (Tem) memory cells in the whole body. In many autoimmune diseases, an elevated level of IL-7 is detected in blood serum and at the site of inflammation, thus suggesting participation of this homeostatic factor in the survival of memory T cells, including auto-reactive clones, in inflammatory disorders. The aim of the study was to investigate the mechanisms of maintaining CD4+ memory T cells under normal and inflammatory conditions. We developed an in vitro model of inflammation, based on induction of pro-inflammatory cytokines, and then evaluated the effects of IL-7 upon purified sorted populations of CD4+Tcm and Tem under normal conditions and in vitro inflammatory model. IL-7 treatment promoted maintenance of CD4+Tcm phenotype in all variants of cultures. In the absence of contact with adherent cell fraction, the IL-7-induced proliferation of Tcm and Tem was slightly reduced, both under normal and inflammatory conditions, thus suggesting low sensitivity of memory T cells to contacts with MHC, and, probably, a requirement for additional signals to provide complete stimulation with IL-7. The last suggestion is also supported by data about CD127 and CD132 expression, i.e., in the absence of contact with MHC, the proportion of CD127+CD132+ cells was decreased in both subpopulations of CD4+ memory cells. Upon in vitro cultures, IL-7 contributed to decreased expression of CD127, and increased expression of CD132 on CD4+Tcm and Tem. We have evaluated the CD4+Tcm and Tem populations by affinity of T cell receptor (TCR), using the level of CD5 expression. Т cells with high TCR affinity for self-antigens are known to have higher expression of CD5. In comparison to Tem, the Tcm contained more CD5high cells. In cultures, IL-7 promoted a high level of CD5 expression on Tcm, which was comparable to levels observed in peripheral blood cells. High CD5 expression on Tem was observed after stimulation with IL-7 in the in vitro inflammatory model. In the absence of contact with MHC, the number of CD5high cells decreased among CD4+Tem and Tcm. Thus, CD4+Tcm cells with high affinity for autologous antigens are probably dependent on the presence of homeostatic factors, in particular, IL-7, and contacts with antigen-presenting cells (APCs). Under conditions of inflammation, no changes were revealed in the mechanism of maintaining CD4+Tcm, in contrast to CD4+Tem. Being less dependent on IL-7 under normal conditions, CD4+CD5highTem are accumulated in the presence of IL-7 under in vitro inflammatory conditions.

The discordant immunologic response to antiretroviral therapy in HIV-infected patients is characterized by ineffective recovery of CD4+T cell counts. The role of regulatory T cells in discordant response to the treatment remains poorly understood both due to the lack of specific and reliable markers of regulatory T cells and their subset’s heterogeneity. In the present work, we studied two groups of HIV-infected patients receiving antiretroviral therapy for more than two years and thus having their viral load suppressed (less than 50 copies of HIV per ml of blood): those who responded (n = 22) and did not respond (n = 19) to the treatment with an increase in their CD4+T cell counts. The control group consisted of uninfected volunteers (n = 23). The CD4+T lymphocyte subset composition was examined by flow cytometry. It was shown that in HIV-infected patients with ineffective immune recovery compared with subjects having a standard response to antiretroviral therapy, the absolute counts of regulatory T cells, as well as CD4+T lymphocytes, was reduced in all maturational subsets: naive cells, central memory, effector memory, and terminally differentiated effectors. That differed immunological nonresponders from patients with a standard response to the treatment, which had a shortage only in naive and central memory regulatory T cell subsets. It is important to note that in HIV-infected patients with a discordant response to therapy, the proportion of effector memory regulatory T cells, that posses the most prominent suppressive capacity, was significantly increased compared with that in other CD4+T lymphocyte subsets. Apparently, despite of regulatory T cell deficiency, in HIV-infected patients with a discordant response to the treatment, the regulatory T cell pool size is big enough to control CD4+T lymphocyte activation. Nevertheless, the number of regulatory T cells may not be sufficient to suppress the over-activation of immunocompetent cells that are not in the CD4+T lymphocyte subset. This can partly explain the increased cell activation level in patients with a discordant response to therapy as compared with those who have a standard respond to the treatment.

Effect of γс-cytokines (IL-2, IL-7 и IL-15) upon maturation and differentiation of cytotoxic and helper CD45RО+ Tcell population was studied in the homeostatic in vitro culture conditions. We have found that IL-2, IL-7 and IL-15 mediate maturation and differentiation of CD8 T cells central memory, replenishing the population of cells that exhibit effector functions. Action of IL-2 on CD4+ central memory T cells is accociated with generation of effector memory cells by reducing the number of immature effectors (CD62L–CD27+), whereas IL-7 promotes the formation of immature (CD62L–CD27+) effectors. IL-2, IL-7 and IL-15 initiate formation of terminally-differentiated cells in a subpopulation of CD8+CD45RO+ lymphocytes, providing a stable immunological memory to a pathogen reinfestation.