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T cell receptor (TCR)-induced death of immature CD4+CD8+ thymocytes by two distinct mechanisms differing in their requirement for CD28 costimulation: implications for negative selection in the thymus.

Punt JA, Havran W, Abe R, Sarin A, Singer A - J. Exp. Med. (1997)

Bottom Line: Negative selection is the process by which the developing lymphocyte receptor repertoire rids itself of autoreactive specificities.One mechanism requires simultaneous TCR and costimulatory signals initiated by CD28.We propose that these mechanisms represent two distinct clonal deletion strategies that are differentially implemented during development depending on whether immature thymocytes encounter antigen in the thymic cortex or thymic medulla.

View Article: PubMed Central - PubMed

Affiliation: Experimental Immunology Branch, National Cancer Institute, Bethesda, Maryland 20892, USA.

ABSTRACT
Negative selection is the process by which the developing lymphocyte receptor repertoire rids itself of autoreactive specificities. One mechanism of negative selection in developing T cells is the induction of apoptosis in immature CD4+CD8+ (DP) thymocytes, referred to as clonal deletion. Clonal deletion is necessarily T cell receptor (TCR) specific, but TCR signals alone are not lethal to purified DP thymocytes. Here, we identify two distinct mechanisms by which TCR-specific death of DP thymocytes can be induced. One mechanism requires simultaneous TCR and costimulatory signals initiated by CD28. The other mechanism is initiated by TCR signals in the absence of simultaneous costimulatory signals and is mediated by subsequent interaction with antigen-presenting cells. We propose that these mechanisms represent two distinct clonal deletion strategies that are differentially implemented during development depending on whether immature thymocytes encounter antigen in the thymic cortex or thymic medulla.

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Characterization of the CD28-independent mechanism of  DP thymocyte apoptosis. DP thymocytes from CD28 KO mice were  presetimulated with platebound anti-TCR antibody for 6 h, then cocultured with APC from either gld mice or B6 Ly5.2 mice in the presence or  absence of the following reagents: anti-FcR antibody (2.4G2, 10 μg/ml);  the fusion protein CD30 Ig (10 μg/ml) which blocks CD30-CD30L interactions; or a combination of anti–B7-1 and anti–B7-2 antibodies (10  μg/ml each) which blocks B7 ligand engagement by both CD28 and  CTLA-4. To compare the effects of various reagents on TCR-CD28– mediated DPthymocyte apoptosis in experiments performed over time,  individual responses were normalized to their respective controls and the  normalized value is referred to as a killing index.
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Figure 8: Characterization of the CD28-independent mechanism of DP thymocyte apoptosis. DP thymocytes from CD28 KO mice were presetimulated with platebound anti-TCR antibody for 6 h, then cocultured with APC from either gld mice or B6 Ly5.2 mice in the presence or absence of the following reagents: anti-FcR antibody (2.4G2, 10 μg/ml); the fusion protein CD30 Ig (10 μg/ml) which blocks CD30-CD30L interactions; or a combination of anti–B7-1 and anti–B7-2 antibodies (10 μg/ml each) which blocks B7 ligand engagement by both CD28 and CTLA-4. To compare the effects of various reagents on TCR-CD28– mediated DPthymocyte apoptosis in experiments performed over time, individual responses were normalized to their respective controls and the normalized value is referred to as a killing index.

Mentions: To determine if fas/ fasL interactions were involved in APC-induced cell death, we prestimulated CD28 KO DP thymocytes with platebound anti-TCR and then transferred them to cultures containing APCs isolated from fasL-deficient (gld) mice (Fig. 8). FasL-deficient APCs from gld mice mediated the death of TCR-stimulated DP thymocytes as efficiently, if not more efficiently, than wild-type APCs (Fig. 8). Thus, the CD28-independent mechanism of TCR-mediated DP cell death is also independent of fas/fasL interactions.


T cell receptor (TCR)-induced death of immature CD4+CD8+ thymocytes by two distinct mechanisms differing in their requirement for CD28 costimulation: implications for negative selection in the thymus.

Punt JA, Havran W, Abe R, Sarin A, Singer A - J. Exp. Med. (1997)

Characterization of the CD28-independent mechanism of  DP thymocyte apoptosis. DP thymocytes from CD28 KO mice were  presetimulated with platebound anti-TCR antibody for 6 h, then cocultured with APC from either gld mice or B6 Ly5.2 mice in the presence or  absence of the following reagents: anti-FcR antibody (2.4G2, 10 μg/ml);  the fusion protein CD30 Ig (10 μg/ml) which blocks CD30-CD30L interactions; or a combination of anti–B7-1 and anti–B7-2 antibodies (10  μg/ml each) which blocks B7 ligand engagement by both CD28 and  CTLA-4. To compare the effects of various reagents on TCR-CD28– mediated DPthymocyte apoptosis in experiments performed over time,  individual responses were normalized to their respective controls and the  normalized value is referred to as a killing index.
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Related In: Results  -  Collection

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Figure 8: Characterization of the CD28-independent mechanism of DP thymocyte apoptosis. DP thymocytes from CD28 KO mice were presetimulated with platebound anti-TCR antibody for 6 h, then cocultured with APC from either gld mice or B6 Ly5.2 mice in the presence or absence of the following reagents: anti-FcR antibody (2.4G2, 10 μg/ml); the fusion protein CD30 Ig (10 μg/ml) which blocks CD30-CD30L interactions; or a combination of anti–B7-1 and anti–B7-2 antibodies (10 μg/ml each) which blocks B7 ligand engagement by both CD28 and CTLA-4. To compare the effects of various reagents on TCR-CD28– mediated DPthymocyte apoptosis in experiments performed over time, individual responses were normalized to their respective controls and the normalized value is referred to as a killing index.
Mentions: To determine if fas/ fasL interactions were involved in APC-induced cell death, we prestimulated CD28 KO DP thymocytes with platebound anti-TCR and then transferred them to cultures containing APCs isolated from fasL-deficient (gld) mice (Fig. 8). FasL-deficient APCs from gld mice mediated the death of TCR-stimulated DP thymocytes as efficiently, if not more efficiently, than wild-type APCs (Fig. 8). Thus, the CD28-independent mechanism of TCR-mediated DP cell death is also independent of fas/fasL interactions.

Bottom Line: Negative selection is the process by which the developing lymphocyte receptor repertoire rids itself of autoreactive specificities.One mechanism requires simultaneous TCR and costimulatory signals initiated by CD28.We propose that these mechanisms represent two distinct clonal deletion strategies that are differentially implemented during development depending on whether immature thymocytes encounter antigen in the thymic cortex or thymic medulla.

View Article: PubMed Central - PubMed

Affiliation: Experimental Immunology Branch, National Cancer Institute, Bethesda, Maryland 20892, USA.

ABSTRACT
Negative selection is the process by which the developing lymphocyte receptor repertoire rids itself of autoreactive specificities. One mechanism of negative selection in developing T cells is the induction of apoptosis in immature CD4+CD8+ (DP) thymocytes, referred to as clonal deletion. Clonal deletion is necessarily T cell receptor (TCR) specific, but TCR signals alone are not lethal to purified DP thymocytes. Here, we identify two distinct mechanisms by which TCR-specific death of DP thymocytes can be induced. One mechanism requires simultaneous TCR and costimulatory signals initiated by CD28. The other mechanism is initiated by TCR signals in the absence of simultaneous costimulatory signals and is mediated by subsequent interaction with antigen-presenting cells. We propose that these mechanisms represent two distinct clonal deletion strategies that are differentially implemented during development depending on whether immature thymocytes encounter antigen in the thymic cortex or thymic medulla.

Show MeSH
Related in: MedlinePlus