Positive selection of T-lymphocytes induced by intrathymic injection of a thymic epithelial cell line

The gene LamC2 encoding the γ2 chain of laminin 5, an epithelial cell-specific extracellular matrix protein, was identified in a PCR-based subtracted cDNA library from mouse thymic stromal cells. The mRNA existed in two alternative forms (5.1 and 2.4 kb). The full-length message was highly expressed in SCID thymus and in a nurse cell line, but not in other thymic epithelial cell lines, while the short form was more widely expressed. In situ hybridization and immunohistochemical staining revealed laminin 5 expression mostly in the subcapsular region of the adult thymus. Addition to fetal thymic organ cultures of a cell adhesion-blocking mAb to the α3 chain of laminin 5 interrupted T cell development. There was a 40% reduction in the total yield of thymocytes, and the most profound decrease (75–90%) was seen in the CD25+CD44+ and CD25+CD44−subsets of the CD4−CD8− double negative fraction. Most of the surviving double negative thymocytes expressed Sca-1, and there were significant increases in the number of cells with CD69 expression and in the fraction of annexin V-stained cells. None of these changes were observed with a nonblocking anti-laminin α3 chain mAb. These results suggest that the interaction between double negative thymoctyes and laminin 5 made by subcapsular epithelial cells is required for the survival and differentiation of mouse thymocytes.

Section: Cdna Clone Tso-2d1 From a Thymic Stromal Cell Library Encodementioning

confidence: 92%

Epithelial Cell-Specific Laminin 5 Is Required for Survival of Early Thymocytes

Kim

Lee

Lee³

et al. 2000

“…Thus, engagement of different costimulatory receptors by their natural ligands can initiate distinct activation responses (maturation and cell death) in TCR-activated DP thymocytes. Positive selection of DP thymocytes has been reported to occur in the thymic cortex in response to TCR signals provided by thymic epithelial cells (4,37,38). This initial activation response may not require CD28 because B7-1 and B7-2 are primarily expressed on epithelial cells and bone marrow-derived APCs in the thymic corticomedullary junction and medulla rather than in the cortex (39 -41).…”

Section: Discussionmentioning

confidence: 99%

CD28 Ligation Costimulates Cell Death but Not Maturation of Double-Positive Thymocytes due to Defective ERK MAPK Signaling

Graham¹,

Bell²,

Huntoon³

et al. 2006

The differentiation of double-positive (DP) CD4+CD8+ thymocytes to single-positive CD4+ or CD8+ T cells is regulated by signals that are initiated by coengagement of the Ag (TCR) and costimulatory receptors. CD28 costimulatory receptors, which augment differentiation and antiapoptotic responses in mature T lymphocytes, have been reported to stimulate both differentiation and apoptotic responses in TCR-activated DP thymocytes. We have used artificial APCs that express ligands for TCR and CD28 to show that CD28 signals increase expression of CD69, Bim, and cell death in TCR-activated DP thymocytes but do not costimulate DP thymocytes to initiate the differentiation program. The lack of a differentiation response is not due to defects in CD28-initiated TCR proximal signaling events but by a selective defect in the activation of ERK MAPK. To characterize signals needed to initiate the death response, a mutational analysis was performed on the CD28 cytoplasmic domain. Although mutation of all of CD28 cytoplasmic domain signaling motifs blocks cell death, the presence of any single motif is able to signal a death response. Thus, there is functional redundancy in the CD28 cytoplasmic domain signaling motifs that initiate the thymocyte death response. In contrast, immobilized Abs can initiate differentiation responses and cell death in DP thymocytes. However, because Ab-mediated differentiation occurs through CD28 receptors with no cytoplasmic domain, the response may be mediated by increased adhesion to immobilized anti-TCR Abs.

“…To determine whether Ube1x 509 -517 is naturally presented, H-2D b molecules were immunopurified from EL-4 lymphoma cells (data not shown), total thymus extract, and the positively selecting thymic epithelial cell line 427.1 (29). The total mixture of eluted peptides was analyzed by MALDI-TOF mass spectrometry.…”

Section: Natural Presentation Of Candidate Peptides By Mhc Class Imentioning

confidence: 99%

Cutting Edge: Positive Selection Induced by a Self-Peptide with TCR Antagonist Activity

Santori

Brown

et al. 2001

Self Cite

Antagonist-like engagement of the TCR has been proposed to induce T cell selection in the thymus. However, no natural TCR ligand with TCR antagonist activity is presently known. Using a combination of bioinformatics and functional testing we identified the first self-peptide that can both deliver antagonist-like signals and promote T cell selection in the thymus. The peptide is presented by appropriate MHC class I molecules in vivo. Thus, endogenous antagonist peptides exist and may be involved in TCR repertoire selection.