T cell activation: you can't get good help

Polymorphisms of the CTLA4 gene and kidney transplant rejection in Korean patients

Cytotoxic T-lymphocyte-associated protein 4 (CTLA4) is a member of the immunoglobulin superfamily. CTLA4, which binds to B7 molecules on antigen- presenting cells, is expressed on activated T cells, thereby delivering negative signals that down-regulate T-cell proliferation and cytokine production. Consequently, CTLA4 may be a good candidate gene to evaluate in kidney transplantation rejection. In this study, we investigated whether polymorphisms of the CTLA4 gene were associated with susceptibility to kidney transplantation rejection. We genotyped three selected SNPs in the CTLA4 gene using direct sequencing in 325 renal transplant recipients. Of the SNPs examined, one (rs231775) showed a statistical association with late acute rejection (p=0.026, odds ratio (OR)=0.48, 95% confidence interval (CI)=0.23-0.93 in the dominant model). Also, the frequency of the G allele (rs231775) was higher in late acute rejection patients (p=0.013, OR=2.02, 95% CI=1.15-3.52). One CTLA4 gene polymorphism was associated with susceptibility to late acute rejection in kidney transplantation in Korean patients.

ICOS-B7 Homologous Protein Interactions Are Necessary for Mercury-Induced Autoimmunity

After exposure to subtoxic doses of heavy metals such as mercury, H-2(s) mice develop an autoimmune syndrome consisting of the rapid production of IgG autoantibodies that are highly specific for nucleolar autoantigens and a polyclonal increase in serum IgG1 and IgE. In this study, we explore the role of one of the members of the CD28-B7 costimulation families, ICOS-B7 homologous protein (B7h), in the regulation of mercury-induced autoimmunity. The expression of ICOS on T cells was more enhanced in susceptible A.SW mice than in non-responsive C57BL/6 and DBA/2 mice after HgCl(2) treatment. Furthermore, in A.SW mice treated with HgCl(2), administration of a blocking anti-ICOS Ab effectively inhibited anti-nucleolar autoantibodies and total serum IgE production. Taken together, these results indicate that the ICOS-B7h costimulation pathway is required for this autoimmune syndrome and suggest that targeting this pathway might have therapeutic benefits for human autoimmune diseases.

PI3-kinase and MAP-kinase signaling cascades in AILIM/ICOS- and CD28-costimulated T-cells have distinct functions between cell proliferation and IL-10 production

Both AILIM/ICOS and CD28 provide positive costimulatory signals for T-cell activation, resulting in proliferation and cytokine production. In this study, we attempted to clarify the key signaling molecules in T-cell proliferation, and also IL-2 and IL-10 production, during T-cell activation by CD3 induced by costimulation with either AILIM/ICOS or CD28. We examined the role of both the PI3-kinase/Akt pathway and MAP kinase family members such as ERK1/2, JNK, and p38 kinase in this process. PI3-kinase and Erk1/2 were shown to potentially regulate primary T-cell activation and subsequent proliferation via both AILIM/ICOS- or CD28-mediated costimulation and the Erk signaling cascade was essential for this proliferation induction and also for IL-2 production. The JAK inhibitor, AG490, inhibited this induction. Our studies indicate that IL-2 is necessary for induction of T-cell proliferation and that the quantities of IL-2 produced by AILIM/ICOS ligation are also sufficient for T-cells to proliferate. In contrast, inhibition of Akt and p38, that are phosphorylated by both AILIM/ICOS and CD28-ligation, could downregulate IL-10 production but not T-cell proliferation. These data raise the interesting possibility that the signaling cascades between T-cell proliferation and IL-10 production are regulated by different molecules in AILIM/ICOS- and CD28-costimulated T-cells.

Involvement of inducible costimulator-B7 homologous protein costimulatory pathway in murine lupus nephritis

Inducible costimulator (ICOS)-B7 homologous protein (B7h) is a new member of the CD28-B7 family of costimulatory molecules that regulates T cell-dependent humoral immune responses. In this study, we examined the involvement of this costimulatory pathway in the development and progression of lupus in NZB/W F(1) mice. Expression of ICOS on T cells was enhanced with disease progression, whereas B7h expression on B cells was down-regulated. Administration of anti-B7h mAb before the onset of renal disease significantly delayed the onset of proteinuria and prolonged survival. Blockade of B7h effectively inhibited all subclasses of IgG autoantibody production and accumulation of both Th1 and Th2 cells. Hypercellularity and deposition of IgG and C3 in glomeruli were significantly reduced. B7h blockade after the onset of proteinuria prevented the disease progression and improved the renal pathology. Our results demonstrated the involvement of the ICOS-B7h costimulatory pathway in the pathogenesis of lupus nephritis, and the blockade of this pathway may be beneficial for the treatment of human systemic lupus erythematosus.

CTLA-4 +49 A/G dimorphism in Italian patients with celiac disease

The chromosome region 2q33, which contains the cytotoxic T lymphocyte antigen-4 (CTLA-4) gene, has been reported in linkage and association with celiac disease (CD). In the present work we have tested the association between the polymorphism of the CTLA-4 exon 1 and susceptibility to CD in an Italian population, using case-control and family-based approaches. The +49 A/G dimorphism was analyzed in 86 patients, 144 ethnically matched controls, and 113 nuclear families by the polymerase chain reaction-restriction fragment length polymorphism method. A significantly higher frequency of the CTLA-4 +49A allele was observed in patients when compared with controls (p = 3 x 10(-2)). The segregation analysis in the 113 trios showed a preferential transmission of the A allele to the probands (chi(2)(TDT) = 4.85). When the patients were stratified according to the presence/absence of the high-risk human leukocyte antigen-DQ2 heterodimer, a significant difference was observed between the two groups, that is, the A allele was increased in the subjects without the DQ2 heterodimer (88.9% vs 73.5%, p = 8.3 x 10(-3)). The A allele was transmitted from heterozygous parents to eight of nine DQ2-dimer-negative patients. These data support CTLA-4 as a predisposing gene for CD in an Italian population with a prominent role in patients not carrying the high-risk human leukocyte antigen-DQ2 molecules.

Modulation of TCR-induced transcriptional profiles by ligation of CD28, ICOS, and CTLA-4 receptors

Signals generated by T cell receptor (TCR) and CD28 engagement are required for optimal T cell activation, but how these signals integrate within the cell is still largely unknown. We have used near genome-scale expression profiling to monitor T cell signal transduction pathways triggered via TCR and/or costimulatory receptors. Ligation of CD28 alone induced a set of short-lived early response transcripts in both Jurkat T cells and primary CD4 T cells, thus providing evidence that CD28 engagement can affect gene regulation independently of TCR engagement. Simultaneous signaling through both the TCR and CD28 resulted in altered expression of several thousand genes following several distinct temporal patterns. Most of these gene regulations were induced by TCR signaling alone and were augmented to varying degrees by CD28 costimulation. CD28 and ICOS costimulation had nearly identical effects on gene regulation, but a few transcripts (e.g., IL2, IL9) were significantly more affected by CD28. Therefore, the distinctive functional outcomes of costimulation via CD28 and ICOS are accompanied by relatively few distinct differences in gene expression. Cytotoxic T lymphocyte antigen 4 (CTLA-4) engagement selectively blocked augmentation of gene regulations by CD28-mediated costimulation, but did not ablate gene regulation induced by TCR triggering alone.

In vivo CD86 blockade inhibits CD4+ T cell activation, whereas CD80 blockade potentiates CD8+ T cell activation and CTL effector function

To address whether a functional dichotomy exists between CD80 and CD86 in naive T cell activation in vivo, we administered anti-CD80 or CD86 blocking mAb alone or in combination to mice with parent-into-F(1) graft-vs-host disease (GVHD). In this model, the injection of naive parental T cells into unirradiated F(1) mice results in either a Th1 cytokine-driven, cell-mediated immune response (acute GVHD) or a Th2 cytokine-driven, Ab-mediated response (chronic GVHD) in the same F(1) recipient. Combined CD80/CD86 blockade beginning at the time of donor cell transfer mimicked previous results seen with CTLA4Ig and completely abrogated either acute or chronic GVHD by preventing the activation and maturation of donor CD4(+) T cells as measured by a block in acquisition of memory marker phenotype and cytokine production. Similar results were seen with selective CD86 blockade; however, the degree of CD4 inhibition was always less than that seen with combined CD80/CD86 blockade. A more striking effect was seen with selective CD80 blockade in that chronic GVHD was converted to acute GVHD. This effect was associated with the induction of Th1 cytokine production, donor CD8(+) T cell activation, and development of antihost CTL. The similarity of this effect to that reported for selective CTLA4 blockade suggests that CD80 is a critical ligand for CTLA4 in mediating the down-regulation of Th1 responses and CD8(+) T cell activation. In contrast, CD86 is critical for the activation of naive CD4(+) T cells in either a Th1 or a Th2 cytokine-mediated response.

The two-signal model of T-cell activation after 30 years

The two-signal model of T-cell activation is still valid after 30 years. The recent understanding of the first signal intricacy and its tight relationship with the second signal have thrown decisive light on T-cell activation processes and the complex molecular events that occur on the surface and within the T cell. Furthermore, the recognition of numerous accessory pathways that, in addition to the CD28 and CD40 pathways, operate to manage antigen-presenting cell T cell cooperation in view of lymphocyte activation, disclose the exquisite and numerous regulatory events that compose the second signal.

Technical note: linkage disequilibrium and disease-associated CTLA4 gene polymorphisms

CTLA4 and CD28 are important regulators of T lymphocyte activation. Gene region 2q33 carrying genes for both CTLA4 and CD28 has been shown to be linked to many autoimmune diseases. Disease associations with particular CTLA4 gene polymorphisms have been reported. Recently, first lines of evidence emerged for functional effects of CTLA4 gene polymorphisms. Two independent studies reported a reduced inhibitory function of CTLA4 in individuals with certain CTLA4 genotypes: those with a high number of microsatellite repeats in one study and those with allele +49*G in exon 1 in the other one. We analyzed the strength of linkage disequilibrium between the three known CTLA4 polymorphisms among 577 independent chromosomes. Our results show that the polymorphisms previously suggested to be the functional risk factors nearly always occur together in a very frequent haplotype. Due to this strong linkage disequilibrium, we conclude that the previous reports studying merely a single polymorphism could not distinguish which variation actually caused the functional difference. Hence, either mutagenesis approaches or studies with data on all linked polymorphisms are still needed to determine the genuine functional risk polymorphism in this gene region.

Sensing pathogens and tuning immune responses

The immune system is capable of making qualitatively distinct responses against different microbial infections, and recent advances are starting to reveal how it manages this complex task. An integral component of the immune system is a network of cells known as dendritic cells (DCs), which sense different microbial stimuli and convey this information to lymphocytes. A better understanding of DC biology has allowed a model to be constructed in which the type of immune response to an infection is viewed as a function of several determinants, including the subpopulation of DCs, the nature of the microbe, microbe recognition receptors, and the cytokine microenvironment.