We investigated the capacity of the Staphylococcal enterotoxin (SE) B, a superantigen (SAg) specific for TCR Vβ domain, to modulate Vβ8+ thymocytes selection in adult mice. Thymocytes were collected at various time intervals after SEB injection (10 and 100 μg) and Vβ8+ modulation was analysed by three color flow cytometry. SEB failed to affect Vβ8+ thymocytes comprised in the less mature compartments, namely, CD4+8+ and CD4-CD8-, whereas it selectively affected Vβ8+CD4+8+ (downward modulation) and Vβ8+CD4-8+ thymocytes (upward modulation). The different response to SEB challenge between CD4+8- and CD4-8+ thymocytes appeared dependent on the CD4/MHC class II interaction, as Vβ8+CD4-8+ thymocytes carrying a transgenic CD4 molecule capable of interacting with MHC class II showed the same response of Vβ8+CD4+8- thymocytes. At variance with thymocytes, however, Vβ8+CD4+8- and Vβ8+CD4-8+ splenic T lymphocytes responded to SAg challenge in identical manner (upward modulation) highlighting the importance of maturation status and/or microenvironment in SAg response. Vβ8+ thymocytes remaining in the thymus were assessed for their capacity to respond to a SAg challenge. Thus, thymocytes were obtained at various time intervals after SEB injection and cultured in the presence of SEB or SEA, a Sag specific for Vβ10 as control. A reduced mitotic response to SEB but not to SEA was noticed irrespective of the number of Vβ8+ responding cells present in culture. It is concluded that SAgs affect TCR specific thymocytes by conditioning their redistribution and inducing an anergic status.

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