V beta-specific deletion of mature thymocytes induced by the plant superantigen Urtica dioica agglutinin

Urtica dioica agglutinin (UDA), a plant protein, is a superantigen activating in a MHC class II-restricted manner the V beta 8.3-bearing T-cells (Galelli and Truffa Bachi, J. Inmunol. 151, 1821, 1993). Administration of UDA to adult mice provokes the clonal expansion of the responding cells which is followed by the deletion of the major fraction of the UDA-sensitive cells, whereas the remaining cells become anergic (Galelli et al., J. Immunol. 154, 2600, 1995), We have analyzed the effect of UDA on thymocytes, Injection of UDA resulted in a rapid, but transient, deletion of a large fraction of the V beta 8.3-bearing mature T-cells. In contrast to other exogenous superantigens, this deletion was not preceded by the clonal expansion of the UDA-responding thymocytes, Moreover, the V beta 8.3-bearing mature T-cells escaping the deletion were not anergic to an in vitro UDA restimulation, UDA and the other superantigens also differ as the general, V beta-unrestricted, thymic atrophy induced by classical superantigens was not observed with UDA. (C) 1996 Academic Press, Inc.