Factors involved in peripheral T cell tolerance: the extent of clonal deletion or clonal anergy depends on the age of the tolerized lymphocytes

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Abstract
After injection of SEB (staphylococcus entero-toxin B), normal adult mice, or thymectomized irradiated mice (TX irr.) reconstituted with lymphocytes taken from normal adult mice became specifically tolerant of SEB. At the same time the percentage of Vβ8 positive CD4 lymphocytes known to be responsive to SEB was almost 50% decreased, indicating that a high level of clonal deletion was realized. In contrast, mice with an exclusively old T cell compartment (old thymectomized mice, TX irr. mice reconstituted several months previously) became tolerant of SEB without deleting their Vβ8 + CD4 + cells, indicating that clonal anergy was the major mechanism in play in the induction of tolerance. Finally, TX irr. mice reconstituted with single positive thymocytes known to become recent thymic emigrants developed tolerance for SEB together with a high level (70%) of clonal deletion. Altogether these results indicated that the mechanism involved in peripheral tolerance depended on the age of the lymphocyte: very young lymphocytes underwent mainly clonal deletion whereas long lived lymphocytes underwent predominantly clonal anergy.