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How many thymocytes audition for selection?

Merkenschlager M, Graf D, Lovatt M, Bommhardt U, Zamoyska R, Fisher AG - J. Exp. Med. (1997)

Bottom Line: T cell maturation requires the rearrangement of clonotypic T cell receptors (TCR) capable of interacting with major histocompatibility complex (MHC) ligands to initiate positive and negative selection.As many as one in five MHC-naive thymocytes show upregulation of activation markers on exposure to MHC-expressing thymic stroma in short-term reaggregate culture.The majority of these cells display physiological changes consistent with entry into the selection process within 24 h.

View Article: PubMed Central - PubMed

Affiliation: Lymphocyte Development Group, Medical Research Council Clinical Sciences Centre, Royal Postgraduate Medical School, Hammersmith Hospital, London W12 0NN, United Kingdom. mmerkens@rpms.ac.uk

ABSTRACT
T cell maturation requires the rearrangement of clonotypic T cell receptors (TCR) capable of interacting with major histocompatibility complex (MHC) ligands to initiate positive and negative selection. Only 3-5% of thymocytes mature to join the peripheral T cell pool. To investigate the basis for this low success rate, we have measured the frequency of preselection thymocytes capable of responding to MHC. As many as one in five MHC-naive thymocytes show upregulation of activation markers on exposure to MHC-expressing thymic stroma in short-term reaggregate culture. The majority of these cells display physiological changes consistent with entry into the selection process within 24 h. By exposing TCR transgenic thymocytes to a range of MHC-peptide complexes, we show that CD69 induction is indicative of thymocyte selection, positive or negative. Our data provide evidence that the fraction of thymocytes that qualify to enter the thymic selection process far exceeds the fraction that successfully complete it, and suggest that most MHC-reactive thymocytes are actively eliminated in the course of selection.

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MHC-naive CD4 T cells respond to MHC. (a) Treatment of  MHC° thymi with CD3/CD4 bispecific antibodies generates CD4 SP  cells phenotypically and functionally similar to CD4 SP cells selected by  MHC class II. (b) Limiting dilution analysis indicates that MHC-naive  and class II–selected CD4 cells mount proliferative responses to allogeneic  CBA/Ca splenocytes with similar frequencies, whereas MHC-naive thymocytes not treated with bispecific antibodies mount no detectable responses. (c) Graphic representation of experiment 2. Shaded areas indicate  95% confidence limits. (d) T cell hybridomas were generated from MHC-naive and class II–selected CD4 cells, and tested for reactivity to a panel of  MHC class II transfected L cells. 8 of 95 (8.4%) and 13 of 99 (13.1%), respectively, responded to at least one class II transfectant, five hybridomas  generated from MHC-naive cells and two hybridomas generated from  class II–selected cells responded to two transfectants.
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Figure 6: MHC-naive CD4 T cells respond to MHC. (a) Treatment of MHC° thymi with CD3/CD4 bispecific antibodies generates CD4 SP cells phenotypically and functionally similar to CD4 SP cells selected by MHC class II. (b) Limiting dilution analysis indicates that MHC-naive and class II–selected CD4 cells mount proliferative responses to allogeneic CBA/Ca splenocytes with similar frequencies, whereas MHC-naive thymocytes not treated with bispecific antibodies mount no detectable responses. (c) Graphic representation of experiment 2. Shaded areas indicate 95% confidence limits. (d) T cell hybridomas were generated from MHC-naive and class II–selected CD4 cells, and tested for reactivity to a panel of MHC class II transfected L cells. 8 of 95 (8.4%) and 13 of 99 (13.1%), respectively, responded to at least one class II transfectant, five hybridomas generated from MHC-naive cells and two hybridomas generated from class II–selected cells responded to two transfectants.

Mentions: Previous estimates suggest that as many as 1–10% of mature, postselection T cells can respond to allogeneic MHC products, and it has been argued that this observation is not readily accounted for by models for thymic selection (17). To explore the nature of this responsiveness to MHC, we attempted a direct comparison of MHC reactivity among MHC-naive and MHC class II–selected CD4 T cells (Fig. 6). Preculture with bispecific (CD3/CD4) antibodies (34) was used to drive thymocyte maturation in the absence of MHC selection (24, 35, 49, 50). In contrast to untreated MHC° thymi, MHC° thymi exposed to CD3/ CD4 bispecific antibodies generated percentages of CD4 SP thymocytes similar to MHC class II+ thymi (Fig. 6 a). Comparing MHC-naive and MHC class II-selected CD4 T cells by limiting dilution analysis, we found similar frequencies of alloreactive cells (1/757 and 1/691 thymocytes, respectively, or 1/621 and 1/587 CD4 cells, Fig. 6, b and c).


How many thymocytes audition for selection?

Merkenschlager M, Graf D, Lovatt M, Bommhardt U, Zamoyska R, Fisher AG - J. Exp. Med. (1997)

MHC-naive CD4 T cells respond to MHC. (a) Treatment of  MHC° thymi with CD3/CD4 bispecific antibodies generates CD4 SP  cells phenotypically and functionally similar to CD4 SP cells selected by  MHC class II. (b) Limiting dilution analysis indicates that MHC-naive  and class II–selected CD4 cells mount proliferative responses to allogeneic  CBA/Ca splenocytes with similar frequencies, whereas MHC-naive thymocytes not treated with bispecific antibodies mount no detectable responses. (c) Graphic representation of experiment 2. Shaded areas indicate  95% confidence limits. (d) T cell hybridomas were generated from MHC-naive and class II–selected CD4 cells, and tested for reactivity to a panel of  MHC class II transfected L cells. 8 of 95 (8.4%) and 13 of 99 (13.1%), respectively, responded to at least one class II transfectant, five hybridomas  generated from MHC-naive cells and two hybridomas generated from  class II–selected cells responded to two transfectants.
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Related In: Results  -  Collection

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Figure 6: MHC-naive CD4 T cells respond to MHC. (a) Treatment of MHC° thymi with CD3/CD4 bispecific antibodies generates CD4 SP cells phenotypically and functionally similar to CD4 SP cells selected by MHC class II. (b) Limiting dilution analysis indicates that MHC-naive and class II–selected CD4 cells mount proliferative responses to allogeneic CBA/Ca splenocytes with similar frequencies, whereas MHC-naive thymocytes not treated with bispecific antibodies mount no detectable responses. (c) Graphic representation of experiment 2. Shaded areas indicate 95% confidence limits. (d) T cell hybridomas were generated from MHC-naive and class II–selected CD4 cells, and tested for reactivity to a panel of MHC class II transfected L cells. 8 of 95 (8.4%) and 13 of 99 (13.1%), respectively, responded to at least one class II transfectant, five hybridomas generated from MHC-naive cells and two hybridomas generated from class II–selected cells responded to two transfectants.
Mentions: Previous estimates suggest that as many as 1–10% of mature, postselection T cells can respond to allogeneic MHC products, and it has been argued that this observation is not readily accounted for by models for thymic selection (17). To explore the nature of this responsiveness to MHC, we attempted a direct comparison of MHC reactivity among MHC-naive and MHC class II–selected CD4 T cells (Fig. 6). Preculture with bispecific (CD3/CD4) antibodies (34) was used to drive thymocyte maturation in the absence of MHC selection (24, 35, 49, 50). In contrast to untreated MHC° thymi, MHC° thymi exposed to CD3/ CD4 bispecific antibodies generated percentages of CD4 SP thymocytes similar to MHC class II+ thymi (Fig. 6 a). Comparing MHC-naive and MHC class II-selected CD4 T cells by limiting dilution analysis, we found similar frequencies of alloreactive cells (1/757 and 1/691 thymocytes, respectively, or 1/621 and 1/587 CD4 cells, Fig. 6, b and c).

Bottom Line: T cell maturation requires the rearrangement of clonotypic T cell receptors (TCR) capable of interacting with major histocompatibility complex (MHC) ligands to initiate positive and negative selection.As many as one in five MHC-naive thymocytes show upregulation of activation markers on exposure to MHC-expressing thymic stroma in short-term reaggregate culture.The majority of these cells display physiological changes consistent with entry into the selection process within 24 h.

View Article: PubMed Central - PubMed

Affiliation: Lymphocyte Development Group, Medical Research Council Clinical Sciences Centre, Royal Postgraduate Medical School, Hammersmith Hospital, London W12 0NN, United Kingdom. mmerkens@rpms.ac.uk

ABSTRACT
T cell maturation requires the rearrangement of clonotypic T cell receptors (TCR) capable of interacting with major histocompatibility complex (MHC) ligands to initiate positive and negative selection. Only 3-5% of thymocytes mature to join the peripheral T cell pool. To investigate the basis for this low success rate, we have measured the frequency of preselection thymocytes capable of responding to MHC. As many as one in five MHC-naive thymocytes show upregulation of activation markers on exposure to MHC-expressing thymic stroma in short-term reaggregate culture. The majority of these cells display physiological changes consistent with entry into the selection process within 24 h. By exposing TCR transgenic thymocytes to a range of MHC-peptide complexes, we show that CD69 induction is indicative of thymocyte selection, positive or negative. Our data provide evidence that the fraction of thymocytes that qualify to enter the thymic selection process far exceeds the fraction that successfully complete it, and suggest that most MHC-reactive thymocytes are actively eliminated in the course of selection.

Show MeSH
Related in: MedlinePlus