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Superantigens: the paradox of T-cell activation versus inactivation
1Institute of Medical Microbiology and Hygiene, Technical University of Munich, Germany.
Superantigens are interesting for several reasons. They exhibit unusual T-cell activation characteristics, they allow to follow in vivo ligand-reactive T cells, they cause T-cell-mediated shock symptoms and they may be causally involved in certain human diseases. This review focuses on the paradox of T-cell activation versus T-cell inactivation as caused by bacterial superantigens in vivo. T-cell activation leads to the acute release of toxic concentrations of lymphokines including tumor necrosis factor alpha/beta, gamma-interferon, interleukin (IL)-2, IL-4 and IL-10. T-cell inactivation mirrors induction of anergy, T-cell receptor downregulation, and that of CD2, CD4 and CD8 cell surface molecules, as well as of apoptosis. Two waves of apoptosis cripple the T-cell repertoire of superantigen-reactive T cells, an immediate one being induced within 24 h and a late one occurring at days 3-4. In between, clonal expansion of anergic ligand-reactive T cells takes place.
Superantigens are interesting for several reasons. They exhibit unusual T-cell activation characteristics, they allow to follow in vivo ligand-reactive T cells, they cause T-cell-mediated shock symptoms and they may be causally involved in certain human diseases. This review focuses on the paradox of T-cell activation versus T-cell inactivation as caused by bacterial superantigens in vivo. T-cell activation leads to the acute release of toxic concentrations of lymphokines including tumor necrosis factor alpha/beta, gamma-interferon, interleukin (IL)-2, IL-4 and IL-10. T-cell inactivation mirrors induction of anergy, T-cell receptor downregulation, and that of CD2, CD4 and CD8 cell surface molecules, as well as of apoptosis. Two waves of apoptosis cripple the T-cell repertoire of superantigen-reactive T cells, an immediate one being induced within 24 h and a late one occurring at days 3-4. In between, clonal expansion of anergic ligand-reactive T cells takes place.