In vivo and in vitro clonal deletion of double-positive thymocytes.

Abstract

StlmrllsryTo study the processes of thymic development, we have established transgenic mice expressing an or/3 T cell antigen receptor (TCK) specific for cytochrome c associated with class II major histocompatibility complex (MHC) molecules. The transgenic TCK chains are expressed by most of the thymocytes in these mice, and these cells have been shown to efficiently mature in association with E L and Ab-encoded class II MHC molecules. This report describes a characterization of the negative selection of these transgenic thymocytes in vivo that is associated with the expression of A s molecules. Negative selection by A s molecules appears to result in the deletion of a late stage of CD4/CD8 double-positive thymocytes in that there is a virtual absence of transgenic TCK bearing CD4 single-positive thymocytes. This phenotype is accompanied by the appearance of CD4/CD8 double-negative thymocytes and peripheral T cells that are functionally antigen reactive. The process of negative selection has also been investigated using an in vitro culture system. Upon presentation of cytochrome c by Eb-expressing nonthymic antigen-presenting cells, there occurs an antigen dose-dependent deletion of the majority of CD4/CD8 double-positive thymocytes. In contrast, presentation of Staphylococcal enterotoxin A by E b in vitro results in minimal deletion of double-positive thymocytes. In addition, we use this in vitro model to examine the effects of cyclosporin A on negative selection. In contrast to its effects on mature T cells, and the findings of others in vivo, cyclosporin A does not inhibit antigen-induced deletion of double-positive thymocytes. Finally, a comparison of the antigen dose responses for thymocyte deletion and for peripheral T cell activation indicates that double-positive thymocyte recognition is more sensitive than mature T cells to antigen recognition. The establishment of immunological self-recognition and tolerance is known to occur primarily in the thymus, where thymocytes undergo a program of differentiation leading to mature functional T cells. Thymocytes are specifically selected based on the specificity of their ot/B TCR. Most of the information currently available relates to the results of thymic selection and not the selection process itself (1); the actual mechanism for selection has yet to be elucidated. T cells that survive thymic selection and are exported to the peripheral lymphoid organs are not overtly self-reactive, yet have the ability to recognize foreign antigenic peptides bound to MHC molecules that are also expressed in the thymus. The selection events that lead to a naive population of T cells specific for foreign peptides bound to self and not foreign alleles of the MHC molecules are termed positive selection; the deletion of T cells overtly reactive to self-MHC molecules, presumably containing self-peptides, is termed negative selection (2). The distinction between the recognition events that lead to positive selection versus negative selection is not understood.The developmental pathwa...

The TNF Receptor Family Member CD30 Is Not Essential for Negative Selection

“…1B and data not shown). Analysis of these mice show that transgenic T cells are positively selected in the H-2 b background, with skewing toward the CD4 ϩ CD8 Ϫ lineage as shown before (23). In the CD30 heterozygous, H-2 s background, negative selection takes place as evidenced by the absence of positive selection and severalfold drop of thymocyte cell number (Fig.…”

“…The AND TCR is specific for pigeon cytochrome c and E k . In transgenic animals, transgene-expressing T cells are positively selected on A b molecule whereas negative selection occurs in the presence of A s (23). Negative selection can also be initiated by injection of pigeon cytochrome c peptide with mice in the H-2 k/b background.…”

“…Subsequent analysis of Nur77-FL mice in CD30 Ϫ/Ϫ background, however, revealed that CD30 does not play a direct role in Nur77-mediated apoptosis in the thymus (22). To confirm the role of CD30 in negative selection, we examined the effect of CD30 mutation on apoptosis mediated by alloreactivity against I-A s in transgenic mice that express the cytochrome c/I-Especific TCR (23). We were surprised to find that the CD30 deficiency failed to rescue thymocytes from negative selection in these AND mice.…”

Graded Deletion and Virus-Induced Activation of Autoreactive CD4+ T Cells

“…There is also evidence that thymocytes that are specific for self peptides which are presented at low levels in the thymus (such as tissue-specific Ags) can, in some cases, evade negative selection and be exported to the periphery (8,9,22). Although these and other studies (23)(24)(25) suggest that negative selection can be sensitive to both the avidity of the autoreactive thymocyte for its cognate self peptide and the amount of self peptide that is presented in the thymus, how these parameters interact to determine the efficiency of negative selection of autoreactive CD4 ϩ T cells in vivo is not well understood.…”

Mature T cell reactivity altered by peptide agonist that induces positive selection.

“…Further studies have demonstrated that even antigens that are unable to activate peripheral T cells expressing a defined T C R can induce TCR-specific thymocyte clonal deletion (50,51). In addition, experiments have shown that less antigen is required for clonal deletion than T cell activation (52,53). One interpretation of these studies has been that the requisite interactions for clonal deletion of thymocytes are less stringent than those required for T cell activation.…”