Positive and Negative CD4+ Thymocyte Selection by a Single MHC Class II/Peptide Ligand Affected by Its Expression Level in the Thymus

Abstract

The central event in thymic selection of T cells bearing alpha beta TCRs is their interaction with self-peptides bound to self-MHC molecules. With the use of transgenic mouse lines expressing a single peptide/MHC class II complex, we show that CD4+ T cells with the preferential usage of particular TCR V(alpha)s and V(beta)s were selected to mature on this complex in lines with the lower expression, whereas such CD4+ T cells were eliminated in the thymus in a line with the relatively high expression. When a low expressing line was crossed with a high expressing line, the frequency of CD4+ T cells selected by this complex markedly decreased. Thus, these results suggest that a single peptide/MHC class II complex, being affected by its cell surface density in the thymus, can serve as both positively and negatively selecting ligand in vivo.

Paradoxical intrathymic positive selection in mice with only a covalently presented agonist peptide

“…In contrast with multiple E␣52-68͞I-A b -specific T hybridomas (20,21) (48,56) and shows that these cells are not antagonized.…”

“…Apoptotic B cells were loaded on immature (day 5-6) DCs 24 hr before stimulation experiments as described (36,37). Although multiple E␣52-68͞I-A b complex-specific T cells specifically react to I-Ab-Ep APCs (20,21), naive 1H3.1 TCR Tg T cells neither produce IL-2 nor proliferate in response to I-Ab-Ep splenocytes (Fig. 1A).…”

Diversity of T cell repertoire shaped by a single peptide ligand is critically affected by its amino acid residue at a T cell receptor contact

“…The gene encoding I-A␤ b chain covalently bound to E␣ chain-derived peptide (E␣52-68; p E␣) has been described elsewhere (13). This construct (PDRp E␣) was modified by PCR to encode lysine at position 58 or 60 of p E␣.…”

“…This was first directly addressed for CD8 ϩ T cells using fetal thymic organ cultures derived from mutant mouse strains where a particular MHC class I-peptide complex is expressed by exogenously adding a given peptide to the culture (6)(7)(8). Subsequently, several groups developed in vivo experimental system focusing on the role of self-peptides in positive selection of CD4 ϩ T cells by creating mouse strains in which all or a large fraction of the MHC class II molecules are occupied with a single peptide (9)(10)(11)(12)(13). With the use of in vitro and in vivo experimental systems, it was shown that limited numbers of self-peptides bound to a given MHC molecule fail to support positive selection of CD8 ϩ or CD4 ϩ T cells expressing a transgenic TCR␣␤ that are selected by the same MHC molecule with a normal array of self-peptides (14)(15)(16)(17)(18)(19).…”

Thymic Selection Generates T Cells Expressing Self-Reactive TCRs in the Absence of CD45

“…TCR signaling may be attenuated in several of the following ways: by decreasing the amount of ligand on the APC or thymic stromal cell (11)(12)(13); by lowering the density of TCR at the surface of the T cell (14); by preventing the relocalization of activated TCRs to the detergent-resistant lipid microdomains of the plasma membrane, which contain elements of the TCR signaling machinery (15); or by altering the quantity or enzymatic activity of signaling molecules recruited by the TCR, such as the Lck protein tyrosine kinase (PTK; Ref. 16).…”