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Caspase-3 is transiently activated without cell death during early antigen driven expansion of CD8(+) T cells in vivo.

McComb S, Mulligan R, Sad S - PLoS ONE (2010)

Bottom Line: Limiting dilution analysis directly showed that in the presence of IL7, very little cell death occurred in both caspase-3(hi) and caspase-3(low) CD8(+) T cells.The expression of active caspase-3 peaked before effector phenotype (CD62L(low)) CD8(+) T cells emerged, and was undetectable in effector-phenotype cells.Our results specifically implicate antigen and not inflammation in driving activation of apoptotic mechanisms without cell death in proliferating CD8(+) T cells.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, NRC-Institute for Biological Sciences, University of Ottawa, Ottawa, Canada.

ABSTRACT

Background: CD8(+) T cell responses develop rapidly during infection and are swiftly reduced during contraction, wherein >90% of primed CD8(+) T cells are eliminated. The role of apoptotic mechanisms in controlling this rapid proliferation and contraction of CD8(+) T cells remains unclear. Surprisingly, evidence has shown non-apoptotic activation of caspase-3 to occur during in vitro T-cell proliferation, but the relevance of these mechanisms to in vivo CD8(+) T cell responses has yet to be examined.

Methods and findings: We have evaluated the activity of caspase-3, a key downstream inducer of apoptosis, throughout the entirety of a CD8(+) T cell response. We utilized two infection models that differ in the intensity, onset and duration of antigen-presentation and inflammation. Expression of cleaved caspase-3 in antigen specific CD8(+) T cells was coupled to the timing and strength of antigen presentation in lymphoid organs. We also observed coordinated activation of additional canonical apoptotic markers, including phosphatidylserine exposure. Limiting dilution analysis directly showed that in the presence of IL7, very little cell death occurred in both caspase-3(hi) and caspase-3(low) CD8(+) T cells. The expression of active caspase-3 peaked before effector phenotype (CD62L(low)) CD8(+) T cells emerged, and was undetectable in effector-phenotype cells. In addition, OVA-specific CD8(+) cells remained active caspase-3(low) throughout the contraction phase.

Conclusions: Our results specifically implicate antigen and not inflammation in driving activation of apoptotic mechanisms without cell death in proliferating CD8(+) T cells. Furthermore, the contraction of CD8(+) T cell response following expansion is likely not mediated by the key downstream apoptosis inducer, caspase-3.

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Related in: MedlinePlus

Caspase 3 and CD62L expression is progressively lost as proliferation proceeds.104 OT1 splenocytes were stained with CFSE and injected in C57BL/6 recipient mice concurrently with LM-OVA challenge. After 3, 4 and 5 days, mice were sacrificed (3 per time point) and spleen cells stained for expression markers. (A) Scatterplots show expression of active caspase-3 versus CFSE and CD62L in OVA-tetramer+ CD8+ T cells after 4 days in vivo. (B) OVA specific CD8+ T cells were gated for division number based on CFSE dilution. Cells show a significant, coordinate decrease in the expression of active caspase-3 and CD62L/IL7Rα as cell proliferation proceeds (***P<0.005, *P<0.05, n = 3 per timepoint).
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pone-0015328-g007: Caspase 3 and CD62L expression is progressively lost as proliferation proceeds.104 OT1 splenocytes were stained with CFSE and injected in C57BL/6 recipient mice concurrently with LM-OVA challenge. After 3, 4 and 5 days, mice were sacrificed (3 per time point) and spleen cells stained for expression markers. (A) Scatterplots show expression of active caspase-3 versus CFSE and CD62L in OVA-tetramer+ CD8+ T cells after 4 days in vivo. (B) OVA specific CD8+ T cells were gated for division number based on CFSE dilution. Cells show a significant, coordinate decrease in the expression of active caspase-3 and CD62L/IL7Rα as cell proliferation proceeds (***P<0.005, *P<0.05, n = 3 per timepoint).

Mentions: To directly examine the mode of caspase-3 activation relative to their proliferation and differentiation, mice were concurrently injected with CFSE stained OT-1 CD8+ T cells and LM-OVA. This allowed the direct observation of proliferation versus the expression of active caspase-3 and differentiation markers at a single time point. Cells that had undergone only a few rounds of division expressed the highest levels of caspase-3, and this was progressively lost as the cells underwent further rounds of division and effector phenotype cells emerged (Fig. 7A, B). These results further support a model wherein caspase-3 is upregulated transiently during the proliferation of recently activated CD8+ T cells, and this apoptotic-like phenotype is progressively lost as cells proliferate further, and differentiated effector cells emerge.


Caspase-3 is transiently activated without cell death during early antigen driven expansion of CD8(+) T cells in vivo.

McComb S, Mulligan R, Sad S - PLoS ONE (2010)

Caspase 3 and CD62L expression is progressively lost as proliferation proceeds.104 OT1 splenocytes were stained with CFSE and injected in C57BL/6 recipient mice concurrently with LM-OVA challenge. After 3, 4 and 5 days, mice were sacrificed (3 per time point) and spleen cells stained for expression markers. (A) Scatterplots show expression of active caspase-3 versus CFSE and CD62L in OVA-tetramer+ CD8+ T cells after 4 days in vivo. (B) OVA specific CD8+ T cells were gated for division number based on CFSE dilution. Cells show a significant, coordinate decrease in the expression of active caspase-3 and CD62L/IL7Rα as cell proliferation proceeds (***P<0.005, *P<0.05, n = 3 per timepoint).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3008739&req=5

pone-0015328-g007: Caspase 3 and CD62L expression is progressively lost as proliferation proceeds.104 OT1 splenocytes were stained with CFSE and injected in C57BL/6 recipient mice concurrently with LM-OVA challenge. After 3, 4 and 5 days, mice were sacrificed (3 per time point) and spleen cells stained for expression markers. (A) Scatterplots show expression of active caspase-3 versus CFSE and CD62L in OVA-tetramer+ CD8+ T cells after 4 days in vivo. (B) OVA specific CD8+ T cells were gated for division number based on CFSE dilution. Cells show a significant, coordinate decrease in the expression of active caspase-3 and CD62L/IL7Rα as cell proliferation proceeds (***P<0.005, *P<0.05, n = 3 per timepoint).
Mentions: To directly examine the mode of caspase-3 activation relative to their proliferation and differentiation, mice were concurrently injected with CFSE stained OT-1 CD8+ T cells and LM-OVA. This allowed the direct observation of proliferation versus the expression of active caspase-3 and differentiation markers at a single time point. Cells that had undergone only a few rounds of division expressed the highest levels of caspase-3, and this was progressively lost as the cells underwent further rounds of division and effector phenotype cells emerged (Fig. 7A, B). These results further support a model wherein caspase-3 is upregulated transiently during the proliferation of recently activated CD8+ T cells, and this apoptotic-like phenotype is progressively lost as cells proliferate further, and differentiated effector cells emerge.

Bottom Line: Limiting dilution analysis directly showed that in the presence of IL7, very little cell death occurred in both caspase-3(hi) and caspase-3(low) CD8(+) T cells.The expression of active caspase-3 peaked before effector phenotype (CD62L(low)) CD8(+) T cells emerged, and was undetectable in effector-phenotype cells.Our results specifically implicate antigen and not inflammation in driving activation of apoptotic mechanisms without cell death in proliferating CD8(+) T cells.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, NRC-Institute for Biological Sciences, University of Ottawa, Ottawa, Canada.

ABSTRACT

Background: CD8(+) T cell responses develop rapidly during infection and are swiftly reduced during contraction, wherein >90% of primed CD8(+) T cells are eliminated. The role of apoptotic mechanisms in controlling this rapid proliferation and contraction of CD8(+) T cells remains unclear. Surprisingly, evidence has shown non-apoptotic activation of caspase-3 to occur during in vitro T-cell proliferation, but the relevance of these mechanisms to in vivo CD8(+) T cell responses has yet to be examined.

Methods and findings: We have evaluated the activity of caspase-3, a key downstream inducer of apoptosis, throughout the entirety of a CD8(+) T cell response. We utilized two infection models that differ in the intensity, onset and duration of antigen-presentation and inflammation. Expression of cleaved caspase-3 in antigen specific CD8(+) T cells was coupled to the timing and strength of antigen presentation in lymphoid organs. We also observed coordinated activation of additional canonical apoptotic markers, including phosphatidylserine exposure. Limiting dilution analysis directly showed that in the presence of IL7, very little cell death occurred in both caspase-3(hi) and caspase-3(low) CD8(+) T cells. The expression of active caspase-3 peaked before effector phenotype (CD62L(low)) CD8(+) T cells emerged, and was undetectable in effector-phenotype cells. In addition, OVA-specific CD8(+) cells remained active caspase-3(low) throughout the contraction phase.

Conclusions: Our results specifically implicate antigen and not inflammation in driving activation of apoptotic mechanisms without cell death in proliferating CD8(+) T cells. Furthermore, the contraction of CD8(+) T cell response following expansion is likely not mediated by the key downstream apoptosis inducer, caspase-3.

Show MeSH
Related in: MedlinePlus