IN THIS ISSUE
http://www.100md.com
免疫学杂志 2005年第14期
Modeling apoptosis
The ability to regulate apoptosis can be useful in treating cancer and autoimmune diseases. Although Fas-induced apoptosis has been extensively studied, complete understanding of the complex interactions of molecules involved in the type I and type II pathways is lacking. Hua et al. (p. 985 ) developed a computational model based on experimental data obtained from studies on human Jurkat cells. The model uses biochemical reactions incorporating 136 rate constants (with 35 independent values) and 15 initial conditions to describe molecular interactions of type I and type II pathway components. Bcl-2 overexpression was predicted to be most effective in blockade of the mitochondrial pathway (type II) under conditions of its binding to two pathway components rather than to either of three single components. Maximum inhibition of caspase-3 activation was seen at a 10-fold increase of Bcl-2 expression in the model and at a 6-fold increase experimentally. Sensitivity analysis, or using the model to predict effects of increasing or decreasing a single component, analyzed the impact of each type I and type II component on caspase-3 activation. A 10- or 100-fold higher concentration of some molecules inhibited caspase-3 activation, whereas lower concentrations of similar magnitude had no effect. Only decreased concentrations of other molecules inhibited capase-3 activation, while both increased and decreased concentrations of a third group of molecules blocked caspase-3 activation. The model, which traces apoptosis from FasL binding through caspase-3 activation, identifies molecular interactions in the type I and type II pathways sensitive to intervention.
Subdominant tumor Ags
The response of CD8+ T cells to foreign Ags varies with the epitope. Understanding factors influencing immunodominance of epitopes could influence vaccine design. Otahal et al. (p. 700 ) transferred naive T cells expressing a TCR specific for the subdominant epitope V of SV40 T Ag (TCR-V) into C57BL/6 mice. Transferred cells were activated and proliferated in mice immunized i.p. with cells transformed with epitope V SV40 T Ag (V-only T Ag); immunization with cells transformed with wild-type SV40 T Ag (wt T Ag) resulted in modest TCR-V T cell proliferation and expansion. TCR-V T cell expansion occurred in mice immunized with a mixture of the two transformed cells but not with cells cotransformed with wt and V-only T Ags. TAP1–/– cells expressing wt or V-only T Ag were not lysed by CTL clones specific for epitope I or epitope V, respectively, unless infected with recombinant vaccinia virus expressing TAP1 and TAP2. In vivo, adoptively transferred naive cells transgenic for epitope I TCR were induced to expand by injected TAP1–/– cells expressing wt T Ag; limited expansion of adoptively transferred TCR-V cells was induced by TAP1–/– cells expressing epitope V and only a small fraction of the cells proliferated. TAP1–/– hosts did not support expansion of TCR-V cells after immunization with cells expressing V-only T Ag. B6 mice immunized with V-only T Ag-expressing cells developed few epitope V-specific CD8+ T cells; however, boosting with wild-type, but not TAP1–/–, cells transformed with V-only or wt T Ag increased epitope V-specific CD8+ T cells 30- and 10-fold, respectively. The authors conclude that subdominance of T Ag epitope V in mice immunized with wt T Ag-transformed cells results from limited cross-presentation of epitope V by APC and competition from immunodominant T Ag epitope-specific CD8+ T cells for T Ag-expressing cells.
Genetic dissection of lupus susceptibility and suppression
Systemic lupus erythematosus (SLE) immune pathology involves abnormal T and B cell development and phenotype, autoantibody production, splenomegaly, and fatal glomerulonephritis. Interactions among several genes determine the likelihood of developing SLE and the severity of the disease. Critical susceptibility regions in mice are defined as Sle1 on chromosome 1, Sle2 on chromosome 4, and Sle3/5 on chromosome 7; the Sles1 locus on mouse chromosome 17 suppresses SLE. These major genomic loci were identified by linkage analysis or through the use of congenic mouse strains carrying NZB or NZW loci on a C57BL/6 (B6) background. However, interactions among these regions in SLE pathogenesis are only partially delineated. In the first of three papers addressing this issue, Wakui et al. (p. 1337 ) transferred congenic bone marrow into sublethally irradiated B6.Rag–/– mice to look at epistatic interactions of regions Sle1 and Sle3/5. Mice receiving cells from B6 mice bicongenic for those two regions had marked splenomegaly exhibiting elevated CD4:CD8 T cell ratios, fewer B cells, greater accumulation of mature B cells at the transition between T1 and T2 cells, and increased numbers of splenic lymphoid dendritic cells along with higher levels of most autoantibodies compared with normal B6 mice. Chimeras of cells monocongenic for either region had values closer to those of normal controls, whereas mice receiving cells from both monocongenic strains had values intermediate to the two groups but closer to those of normal mice. A genetic dissection of the influence of the Sle2 locus on B cell development by Xu et al. (p. 936 ) was accomplished using B6 mice congenic for one of three subintervals, Sle2a, Sle2b, or Sle2c. Older Sle2c congenics had the greatest expansion of B-1a cells in the peritoneal cavity and spleen compared with the other congenic strains and B6 controls; later B1-a cell expansion was seen in Sle2a congenic mice. Reduced surface expression of IgM on B-1a cells of splenic origin mapped to Sle2a. Mice tricongenic for Sle1, Sle3, and Sle2a or Sle2b had more prominent parameters of lupus pathogenesis including extensive remodeling of the splenic architecture with influx of CD11b+ cells in T and B cell zones than animals tricongenic for Sle1, Sle3, and Sle2c. Subramanian et al. (p. 1062 ) used congenic recombinant fine-mapping to introduce six intervals of the NZW Sles1 locus into B6 mice congenic for Sle1. Progeny homozygous, but not heterozygous, for some Sles1 subintervals suppressed SLE splenomegaly, anti-chromatin Ab production, and T and B cell activation. Sles1 gene activity mapped to a 956-kb interval within the Sles locus. The authors discovered a complementary Sles1 modifier allele in 129 mice by creating a 129 x B6 congenic strain homozygous for a specific 129 autoimmunity-promoting region but heterozygous for the suppressive NZW Sles1 allele. Together, these three manuscripts point out the importance of epistatic interactions among SLE genes and the utility of congenic recombinant mouse strains in understanding contributions from specific cell types in this complex genetic disease.
Tolerizing self-reactive B cells
Central tolerance mechanisms for self-reactive B cells involve anergy, deletion, and receptor editing. However, the contribution of each mechanism to limiting self-reactive B cells is unknown. Hippen et al. (p. 909 ) bred mice transgenic for membrane hen egg lysozyme (mHEL) with mice carrying double transgenes (anti-HEL H chain plus anti-HEL L chain knock-in at the endogenous locus). Triple transgenic progeny splenic B cell numbers were equivalent to those in transgenic mice carrying randomly integrated anti-HEL H chain plus anti-HEL L chain, but the cells were unable to bind HEL. In contrast, pre-B cells were clonally deleted in transgenic mHEL mice carrying randomly integrated anti-HEL H chain plus anti-HEL L chain. In lethally irradiated mHEL mice injected with bone marrow from anti-HEL H chain plus anti-HEL L chain knock-in transgenic mice, nearly half of the generated B cells did not bind HEL but expressed a human C chain knock-in transgene marker. Only background levels of B cells positive for the human marker were seen in wild-type recipients. Mice triple transgenic for mHEL, anti-HEL H chain plus anti-HEL L chain knock-in had low levels of serum anti-HEL IgMa Abs compared with controls, and their spleen cells proliferated in response to LPS but not to HEL. Mice triple transgenic for mHEL, anti-HEL H chain plus anti-HEL L chain knock-in had the highest percentage of pre-B cells and a B cell developmental delay of 6 h as demonstrated by BrdU pulse labeling. Mice triple transgenic for soluble HEL, anti-HEL H chain plus anti-HEL L chain knock-in had two populations of splenic B cells. An anergic cell population had low levels of IgMa, no HEL binding, and localized to splenic follicles; a second non-HEL binding population had high levels of IgMa and localized to the marginal zone. The data suggest that receptor editing tolerizes B cells reactive to membrane-bound self Ag, whereas both receptor editing and anergy tolerize B cells reactive to soluble self Ag.
Allogeneic skin graft acceptance
Donor-specific transfusion (DST) of allogeneic cells combined with anti-CD154 Ab induces long-term acceptance of allogeneic skin grafts. Yet the underlying cellular and molecular mechanisms of tolerance in this system are unknown. Quezada et al. (p. 771 ) transfused C57BL/6 mice with TCR transgenic (Tg) CD4+ T cells (TEa-Tg) that recognized a major alloantigen on F1 skin grafted 7 days later. Mice given DST plus anti-CD154 Ab at the time of cell transfer accepted skin grafts long-term; grafts were not retained by treated recipients depleted of CD4+CD25+ regulatory T cells (Treg) with anti-CD25 mAb, costimulated with anti-GITR (glucocorticoid-induced TNFR-related gene) Ab, or untreated. TEa-Tg cell expansion in mice given DST plus control hamster Ig at the time of transfer was greater than in mice given DST plus anti-CD154 Ab. Synthesis of IL-2 and IFN- was blocked in transfused CFSE-TEa-Tg cells 5 days after DST plus anti-CD154 Ab treatment. Mice tolerized with DST plus anti-CD154 Ab rejected 45-day-old skin grafts after anti-GITR treatment. Naive TEa-Tg cells adoptively transferred into mice tolerized by DST plus anti-CD154 Ab treatment 3 wk earlier had reduced capacity to expand, differentiate, produce cytokines, and reject F1 skin grafted at the time of transfer compared with TEa-Tg cells given to nontolerized recipients. Anti-GITR or anti-CD40 Ab partially reversed the tolerant state. The data suggest that both effector T cell suppression by Treg cells and anergy induced by costimulation blockade contribute to tolerance of allogeneic skin grafts.
Understanding oral tolerance
Oral tolerance, a form of peripheral tolerance to non-self Ags, is induced by oral administration of soluble Ags and is mediated by hyporesponsive T cells. However, the ability of tolerized T cells to form conjugates and immunological synapses with APCs had not been investigated. Ise et al. (p. 829 ) developed in vivo tolerized T cells by giving OVA in drinking water to OVA-TCR transgenic mice. Splenic CD4+ T cells from OVA-fed mice had reduced OVA-induced proliferation and IL-2 production, and the mice had lower anti-OVA IgG serum levels than untreated controls. Splenic CD4+ T cells from OVA fed mice formed LFA-1/ICAM-1 integrin-dependent conjugates with OVA-pulsed T cell-depleted splenocytes at comparable levels with splenic T cells from untreated mice. However, Ag-stimulated orally-tolerized T cells had impaired formation of immunological synapses with APCs, i.e., less TCR and protein kinase C- were associated with lipid raft fractions. Lower levels of the phosphorylated GTPases, Rac1 and cdc42, and the guanine nucleotide exchange factor, Vav, were found in orally-tolerized T cells than in untreated T cells after OVA stimulation. By contrast, OVA-immunized T cells had proliferation, IL-2 production, conjugate formation and Ag-induced activation of Vav, Rac1, and cdc42 equivalent to untreated T cells. The authors conclude that orally-tolerized T cells can form stable conjugates with APCs but, unlike OVA-immunized T cells, have impaired immunological synapse formation.
Summaries written by Dorothy L. Buchhagen, Ph.D.
Related articles in The JI:
Genetic Dissection of Systemic Lupus Erythematosus Pathogenesis: Partial Functional Complementation between Sle1 and Sle3/5 Demonstrates Requirement for Intracellular Coexpression for Full Phenotypic Expression of Lupus
Masatoshi Wakui, Laurence Morel, Edward J. Butfiloski, Chunsun Kim, and Eric S. Sobel
The JI 2005 175: 1337-1345.
Inefficient Cross-Presentation Limits the CD8+ T Cell Response to a Subdominant Tumor Antigen Epitope
Pavel Otahal, Sandra C. Hutchinson, Lawrence M. Mylin, M. Judith Tevethia, Satvir S. Tevethia, and Todd D. Schell
Analysis of the Underlying Cellular Mechanisms of Anti-CD154-Induced Graft Tolerance: The Interplay of Clonal Anergy and Immune Regulation
Sergio A. Quezada, Kathy Bennett, Bruce R. Blazar, Alexander Y. Rudensky, Shimon Sakaguchi, and Randolph J. Noelle
The ability to regulate apoptosis can be useful in treating cancer and autoimmune diseases. Although Fas-induced apoptosis has been extensively studied, complete understanding of the complex interactions of molecules involved in the type I and type II pathways is lacking. Hua et al. (p. 985 ) developed a computational model based on experimental data obtained from studies on human Jurkat cells. The model uses biochemical reactions incorporating 136 rate constants (with 35 independent values) and 15 initial conditions to describe molecular interactions of type I and type II pathway components. Bcl-2 overexpression was predicted to be most effective in blockade of the mitochondrial pathway (type II) under conditions of its binding to two pathway components rather than to either of three single components. Maximum inhibition of caspase-3 activation was seen at a 10-fold increase of Bcl-2 expression in the model and at a 6-fold increase experimentally. Sensitivity analysis, or using the model to predict effects of increasing or decreasing a single component, analyzed the impact of each type I and type II component on caspase-3 activation. A 10- or 100-fold higher concentration of some molecules inhibited caspase-3 activation, whereas lower concentrations of similar magnitude had no effect. Only decreased concentrations of other molecules inhibited capase-3 activation, while both increased and decreased concentrations of a third group of molecules blocked caspase-3 activation. The model, which traces apoptosis from FasL binding through caspase-3 activation, identifies molecular interactions in the type I and type II pathways sensitive to intervention.
Subdominant tumor Ags
The response of CD8+ T cells to foreign Ags varies with the epitope. Understanding factors influencing immunodominance of epitopes could influence vaccine design. Otahal et al. (p. 700 ) transferred naive T cells expressing a TCR specific for the subdominant epitope V of SV40 T Ag (TCR-V) into C57BL/6 mice. Transferred cells were activated and proliferated in mice immunized i.p. with cells transformed with epitope V SV40 T Ag (V-only T Ag); immunization with cells transformed with wild-type SV40 T Ag (wt T Ag) resulted in modest TCR-V T cell proliferation and expansion. TCR-V T cell expansion occurred in mice immunized with a mixture of the two transformed cells but not with cells cotransformed with wt and V-only T Ags. TAP1–/– cells expressing wt or V-only T Ag were not lysed by CTL clones specific for epitope I or epitope V, respectively, unless infected with recombinant vaccinia virus expressing TAP1 and TAP2. In vivo, adoptively transferred naive cells transgenic for epitope I TCR were induced to expand by injected TAP1–/– cells expressing wt T Ag; limited expansion of adoptively transferred TCR-V cells was induced by TAP1–/– cells expressing epitope V and only a small fraction of the cells proliferated. TAP1–/– hosts did not support expansion of TCR-V cells after immunization with cells expressing V-only T Ag. B6 mice immunized with V-only T Ag-expressing cells developed few epitope V-specific CD8+ T cells; however, boosting with wild-type, but not TAP1–/–, cells transformed with V-only or wt T Ag increased epitope V-specific CD8+ T cells 30- and 10-fold, respectively. The authors conclude that subdominance of T Ag epitope V in mice immunized with wt T Ag-transformed cells results from limited cross-presentation of epitope V by APC and competition from immunodominant T Ag epitope-specific CD8+ T cells for T Ag-expressing cells.
Genetic dissection of lupus susceptibility and suppression
Systemic lupus erythematosus (SLE) immune pathology involves abnormal T and B cell development and phenotype, autoantibody production, splenomegaly, and fatal glomerulonephritis. Interactions among several genes determine the likelihood of developing SLE and the severity of the disease. Critical susceptibility regions in mice are defined as Sle1 on chromosome 1, Sle2 on chromosome 4, and Sle3/5 on chromosome 7; the Sles1 locus on mouse chromosome 17 suppresses SLE. These major genomic loci were identified by linkage analysis or through the use of congenic mouse strains carrying NZB or NZW loci on a C57BL/6 (B6) background. However, interactions among these regions in SLE pathogenesis are only partially delineated. In the first of three papers addressing this issue, Wakui et al. (p. 1337 ) transferred congenic bone marrow into sublethally irradiated B6.Rag–/– mice to look at epistatic interactions of regions Sle1 and Sle3/5. Mice receiving cells from B6 mice bicongenic for those two regions had marked splenomegaly exhibiting elevated CD4:CD8 T cell ratios, fewer B cells, greater accumulation of mature B cells at the transition between T1 and T2 cells, and increased numbers of splenic lymphoid dendritic cells along with higher levels of most autoantibodies compared with normal B6 mice. Chimeras of cells monocongenic for either region had values closer to those of normal controls, whereas mice receiving cells from both monocongenic strains had values intermediate to the two groups but closer to those of normal mice. A genetic dissection of the influence of the Sle2 locus on B cell development by Xu et al. (p. 936 ) was accomplished using B6 mice congenic for one of three subintervals, Sle2a, Sle2b, or Sle2c. Older Sle2c congenics had the greatest expansion of B-1a cells in the peritoneal cavity and spleen compared with the other congenic strains and B6 controls; later B1-a cell expansion was seen in Sle2a congenic mice. Reduced surface expression of IgM on B-1a cells of splenic origin mapped to Sle2a. Mice tricongenic for Sle1, Sle3, and Sle2a or Sle2b had more prominent parameters of lupus pathogenesis including extensive remodeling of the splenic architecture with influx of CD11b+ cells in T and B cell zones than animals tricongenic for Sle1, Sle3, and Sle2c. Subramanian et al. (p. 1062 ) used congenic recombinant fine-mapping to introduce six intervals of the NZW Sles1 locus into B6 mice congenic for Sle1. Progeny homozygous, but not heterozygous, for some Sles1 subintervals suppressed SLE splenomegaly, anti-chromatin Ab production, and T and B cell activation. Sles1 gene activity mapped to a 956-kb interval within the Sles locus. The authors discovered a complementary Sles1 modifier allele in 129 mice by creating a 129 x B6 congenic strain homozygous for a specific 129 autoimmunity-promoting region but heterozygous for the suppressive NZW Sles1 allele. Together, these three manuscripts point out the importance of epistatic interactions among SLE genes and the utility of congenic recombinant mouse strains in understanding contributions from specific cell types in this complex genetic disease.
Tolerizing self-reactive B cells
Central tolerance mechanisms for self-reactive B cells involve anergy, deletion, and receptor editing. However, the contribution of each mechanism to limiting self-reactive B cells is unknown. Hippen et al. (p. 909 ) bred mice transgenic for membrane hen egg lysozyme (mHEL) with mice carrying double transgenes (anti-HEL H chain plus anti-HEL L chain knock-in at the endogenous locus). Triple transgenic progeny splenic B cell numbers were equivalent to those in transgenic mice carrying randomly integrated anti-HEL H chain plus anti-HEL L chain, but the cells were unable to bind HEL. In contrast, pre-B cells were clonally deleted in transgenic mHEL mice carrying randomly integrated anti-HEL H chain plus anti-HEL L chain. In lethally irradiated mHEL mice injected with bone marrow from anti-HEL H chain plus anti-HEL L chain knock-in transgenic mice, nearly half of the generated B cells did not bind HEL but expressed a human C chain knock-in transgene marker. Only background levels of B cells positive for the human marker were seen in wild-type recipients. Mice triple transgenic for mHEL, anti-HEL H chain plus anti-HEL L chain knock-in had low levels of serum anti-HEL IgMa Abs compared with controls, and their spleen cells proliferated in response to LPS but not to HEL. Mice triple transgenic for mHEL, anti-HEL H chain plus anti-HEL L chain knock-in had the highest percentage of pre-B cells and a B cell developmental delay of 6 h as demonstrated by BrdU pulse labeling. Mice triple transgenic for soluble HEL, anti-HEL H chain plus anti-HEL L chain knock-in had two populations of splenic B cells. An anergic cell population had low levels of IgMa, no HEL binding, and localized to splenic follicles; a second non-HEL binding population had high levels of IgMa and localized to the marginal zone. The data suggest that receptor editing tolerizes B cells reactive to membrane-bound self Ag, whereas both receptor editing and anergy tolerize B cells reactive to soluble self Ag.
Allogeneic skin graft acceptance
Donor-specific transfusion (DST) of allogeneic cells combined with anti-CD154 Ab induces long-term acceptance of allogeneic skin grafts. Yet the underlying cellular and molecular mechanisms of tolerance in this system are unknown. Quezada et al. (p. 771 ) transfused C57BL/6 mice with TCR transgenic (Tg) CD4+ T cells (TEa-Tg) that recognized a major alloantigen on F1 skin grafted 7 days later. Mice given DST plus anti-CD154 Ab at the time of cell transfer accepted skin grafts long-term; grafts were not retained by treated recipients depleted of CD4+CD25+ regulatory T cells (Treg) with anti-CD25 mAb, costimulated with anti-GITR (glucocorticoid-induced TNFR-related gene) Ab, or untreated. TEa-Tg cell expansion in mice given DST plus control hamster Ig at the time of transfer was greater than in mice given DST plus anti-CD154 Ab. Synthesis of IL-2 and IFN- was blocked in transfused CFSE-TEa-Tg cells 5 days after DST plus anti-CD154 Ab treatment. Mice tolerized with DST plus anti-CD154 Ab rejected 45-day-old skin grafts after anti-GITR treatment. Naive TEa-Tg cells adoptively transferred into mice tolerized by DST plus anti-CD154 Ab treatment 3 wk earlier had reduced capacity to expand, differentiate, produce cytokines, and reject F1 skin grafted at the time of transfer compared with TEa-Tg cells given to nontolerized recipients. Anti-GITR or anti-CD40 Ab partially reversed the tolerant state. The data suggest that both effector T cell suppression by Treg cells and anergy induced by costimulation blockade contribute to tolerance of allogeneic skin grafts.
Understanding oral tolerance
Oral tolerance, a form of peripheral tolerance to non-self Ags, is induced by oral administration of soluble Ags and is mediated by hyporesponsive T cells. However, the ability of tolerized T cells to form conjugates and immunological synapses with APCs had not been investigated. Ise et al. (p. 829 ) developed in vivo tolerized T cells by giving OVA in drinking water to OVA-TCR transgenic mice. Splenic CD4+ T cells from OVA-fed mice had reduced OVA-induced proliferation and IL-2 production, and the mice had lower anti-OVA IgG serum levels than untreated controls. Splenic CD4+ T cells from OVA fed mice formed LFA-1/ICAM-1 integrin-dependent conjugates with OVA-pulsed T cell-depleted splenocytes at comparable levels with splenic T cells from untreated mice. However, Ag-stimulated orally-tolerized T cells had impaired formation of immunological synapses with APCs, i.e., less TCR and protein kinase C- were associated with lipid raft fractions. Lower levels of the phosphorylated GTPases, Rac1 and cdc42, and the guanine nucleotide exchange factor, Vav, were found in orally-tolerized T cells than in untreated T cells after OVA stimulation. By contrast, OVA-immunized T cells had proliferation, IL-2 production, conjugate formation and Ag-induced activation of Vav, Rac1, and cdc42 equivalent to untreated T cells. The authors conclude that orally-tolerized T cells can form stable conjugates with APCs but, unlike OVA-immunized T cells, have impaired immunological synapse formation.
Summaries written by Dorothy L. Buchhagen, Ph.D.
Related articles in The JI:
Genetic Dissection of Systemic Lupus Erythematosus Pathogenesis: Partial Functional Complementation between Sle1 and Sle3/5 Demonstrates Requirement for Intracellular Coexpression for Full Phenotypic Expression of Lupus
Masatoshi Wakui, Laurence Morel, Edward J. Butfiloski, Chunsun Kim, and Eric S. Sobel
The JI 2005 175: 1337-1345.
Inefficient Cross-Presentation Limits the CD8+ T Cell Response to a Subdominant Tumor Antigen Epitope
Pavel Otahal, Sandra C. Hutchinson, Lawrence M. Mylin, M. Judith Tevethia, Satvir S. Tevethia, and Todd D. Schell
Analysis of the Underlying Cellular Mechanisms of Anti-CD154-Induced Graft Tolerance: The Interplay of Clonal Anergy and Immune Regulation
Sergio A. Quezada, Kathy Bennett, Bruce R. Blazar, Alexander Y. Rudensky, Shimon Sakaguchi, and Randolph J. Noelle