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. Immunol. 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.