The fourth way? Harnessing aggressive tendencies in the thymus.
During late stages of thymic development, T cells must chose between different fates, dictated by their TCR specificity. Typically, this is thought of as a choice between three alternatives (being positive selection for useful T cells vs negative selection or neglect for harmful or useless T cells). However, there is growing evidence for a fourth alternative, in which T cells are positively selected by agonist ligands, which would normally be expected to induce T cell deletion. In this review, we will discuss where and when agonist selection is induced and whether this should be considered as a novel form of thymic selection or as an alternative differentiation state for Ag-exposed T cells.
Baldwin
Troy A
TA
Center for Immunology, Department of Laboratory Medicine and Pathology, University of Minnesota, Minneapolis, MN 55455, USA.
Hogquist
Kristin A
KA
Jameson
Stephen C
SC
D002454:Cell Differentiation / Q000276:immunology; D016693:Receptors, Antigen, T-Cell, alpha-beta / Q000819:agonists* / Q000502:physiology; D016176:T-Lymphocyte Subsets / Q000166:cytology* / Q000276:immunology / Q000378:metabolism*; D013950:Thymus Gland / Q000166:cytology* / Q000276:immunology / Q000378:metabolism*
D016693:Receptors, Antigen, T-Cell, alpha-beta