Effects of exogenous IL-2 administration on the homeostasis of CD4+ T lymphocytes

Arnaud Foussat1, Laurence Bouchet-Delbos, Jacques Couderc

  • 1INSERM U131, Cytokines et Immunorégulation, Hêpital Antoine Béclère, Assistance Publique-Hêpitaux de Paris, Institut Paris-Sud sur les Cytokines, 92140 Clamart, France.

IL-2 is currently used in HIV-infected patients to treat CD4+ T lymphopenia. In order to document a mechanism accounting for its capacity to restore immune function, we studied the effects of IL-2 administration in mice. IL-2 treatment of C57BL/6 mice for 4 days leads to a transient accumulation of CD4+ T lymphocytes. Whereas memory and activated CD4+ T lymphocytes accumulate after IL-2 treatment in both lymphoid and nonlymphoid organs, naive CD4+ T cells only accumulate in the former. IL-2 transiently increases CD4+ T lymphocyte numbers in lymphopenic IL-7(-/-) mice. Studies in T-cell-reconstituted Rag(-/-) gamma c(-/-) mice and in thymectomized mice demonstrated that IL-2 acts directly on peripheral CD4+ T lymphocytes. In vivo labeling of thymocytes showed that IL-2 also stimulates the release of CD4+ thymocytes from the thymus. Therefore, IL-2 treatment acts centrally and peripherally to increase the size of the naive CD4+ T lymphocyte compartment. This dual activity of IL-2 treatment may influence the quality of restoration of this compartment, especially regarding the ability to reconstitute a normal T lymphocyte repertoire.

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