The natural course of HIV infection causes a severe depletion of CD4+ T cells, phenotypic alterations of T-cell subsets and a decline in thymic function, which in turn produces a progressive impairment of the immune function. HIVinfected children present some distinct features when compared to adults mainly due to the immaturity of immune system and the preserved capacity of thymic renewal of immune cells. The introduction of highly active antiretroviral therapy (HAART) decreased mortality rates in HIV-infected children, and proved to be effective in suppressing plasma viral loads and increasing CD4+ T-cell counts and T-cell rearrangement excision circles (TREC) levels in young HIV-infected patients. These findings indicate that recovery of thymic function is a pivotal event in immune reconstitution. Among the cytokines and hormones identified as possible regulators of thymopoiesis, IL-7 may play an essential role promoting the differentiation of thymocytes into mature T cells that will leave the thymus and move to the periphery in response to Tcell depletion. HAART provides appropriate functional immune reconstitution in children to withdraw prophylaxis against some opportunistic infections, but a revaccination or antigenic reexposure could be required to restore the protective immunity to some vaccine-preventable diseases. The immune reconstitution associated to HAART could also produce an immune reconstitution inflammatory syndrome (IRIS). In conclusion, HAART treatment in HIV-infected children has shown to be effective in decreasing viral load (VL) and recovering the T-cell population due to a preserved thymic function as well as the homeostatic mechanisms of IL-7.
Keywords: HIV, children, immune reconstitution, HAART, thymus, IRIS
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