Deep sequencing of the TCR-ß repertoire of human forkhead box protein 3 (FoxP3)+ and FoxP3- T cells suggests that they are completely distinct and non-overlapping.

Maintenance of peripheral tolerance requires a balance between autoreactive conventional T cells (Tconv ) and thymically derived forkhead box protein 3 (FoxP3)+ regulatory T cells (tTregs ). Considerable controversy exists regarding the similarities/differences in T cell receptor (TCR) repertoires expressed by Tconv and tTregs . We generated highly purified populations of human adult and cord blood Tconv and tTregs based on the differential expression of CD25 and CD127. The purity of the sorted populations was validated by intracellular staining for FoxP3 and Helios. We also purified an overlap group of CD4 T cells from adult donors to ensure that considerable numbers of shared clonotypes could be detected when present. We used deep sequencing of entire TCR-ß CDR3 sequences to analyse the TCR repertoire of Tconv and tTregs . Our studies suggest that both neonatal and adult human Tconv and tTreg cells are, in fact, entirely distinct CD4 T cell lineages.

Spatial genome organization during T-cell differentiation.

The spatial organization of genomes within the mammalian cell nucleus is non-random. The functional relevance of spatial genome organization might be in influencing gene expression programs as cells undergo changes during development and differentiation. To gain insight into the plasticity of genomes in space and time and to correlate the activity of specific genes with their nuclear position, we systematically analyzed the spatial genome organization in differentiating mouse T-cells. We find significant global reorganization of centromeres, chromosomes and gene loci during the differentiation process. Centromeres were repositioned from a preferentially internal distribution in undifferentiated cells to a preferentially peripheral position in differentiated CD4+ and CD8+ cells. Chromosome 6, containing the differentially expressed T-cell markers CD4 and CD8, underwent differential changes in position depending on whether cells differentiated into CD4+ or CD8+ thymocytes. Similarly, the two marker loci CD4 and CD8 showed distinct behavior in their position relative to the chromosome 6 centromere at various stages of differentiation. Our results demonstrate that significant spatial genome reorganization occurs during differentiation and indicate that the relationship between dynamic genome topology and single gene regulation is highly complex.

Control of T-cell activation by CD4+ CD25+ suppressor T cells.

Depletion of the minor ( approximately 10%) subpopulation of CD4+ T cells that co-expresses CD25 (interleukin (IL)-2 receptor alpha-chain) by thymectomy of neonates on the third day of life or by treatment of adult CD4+ T cells with anti-CD25 and complement results in the development of organ-specific autoimmunity. Autoimmune disease can be prevented by reconstitution of the animals with CD4+ CD25+ cells. CD4+ CD25+-mediated protection of autoimmune gastritis does not require the suppressor cytokines IL-4, IL-10, or transforming growth factor (TGF)-beta. Mice that express a transgenic T-cell receptor (TCR) derived from a thymectomized newborn that recognizes the gastric parietal cell antigen H/K ATPase all develop severe autoimmune gastritis very early in life. CD4+ CD25+ T cells are also powerful suppressors of the activation of both CD4+ and CD8+ T cells in vitro. Suppression is mediated by a cell contact-dependent, cytokine-independent T-T interaction. Activation of CD4+ CD25+ via their TCR generates suppressor effector cells that are capable of non-specifically suppressing the activation of any CD4+ or CD8+ T cell. Activation of suppressor effector function is independent of co-stimulation mediated by CD28/CTLA-4 interactions with CD80/CD86. We propose that CD4+ CD25+ T cells recognize organ-specific antigens, are recruited to sites of autoimmune damage where they are activated by their target antigen, and then physically interact with autoreactive CD4+ or CD8+ effector cells to suppress the development of autoimmune disease.

Inhibition of the function of the FcgammaRIIB by a monoclonal antibody to thymic shared antigen-1, a Ly-6 family antigen.

Thymic shared antigen-1 (TSA-1) is a member of the Ly-6 family of glycosyl-phosphatidylinositol (GPI)-linked proteins. While it has been proposed that TSA-1 may play a role in thymic development, a physiological ligand for this antigen has not been identified. Here we report that a monoclonal antibody (mAb) to TSA-1, generated by immunizing a hamster with CD40 ligand (CD40L)-activated B cells, interferes with the function of FcgammaRIIB on splenic B cells and the B-cell lymphoma cell line, M12, by binding to TSA on the same cells. The interaction of anti-TSA with FcgammaRIIB resulted in an inhibition of the ability of the FcgammaRIIB to cross-link and/or aggregate soluble anti-CD3 or soluble anti-Cbeta T-cell receptor (TCR), leading to an inhibition of induction of expression of CD25 and CD69, interleukin (IL)-2 production and proliferation of naive T cells. Cross-blocking studies with mAbs strongly suggested that a physical association exists between TSA-1 and the FcgammaRIIB on the surface of activated B cells and favour the view that a functional intermolecular association exists between these two distinct membrane antigens.

Control of organ-specific autoimmunity by immunoregulatory CD4(+)CD25(+) T cells.

CD4(+)CD25(+) T cells regulate the activity of autoreactive T cells. Depletion of these cells results in the development of a wide-spectrum of organ-specific autoimmune diseases. In vitro model systems have been developed to study the function of these potent suppressor cells. Following their activation via their T-cell receptor, they downregulate the responses of CD25(-) effectors by a T-T interaction.

Regulation of interleukin (IL)-18 receptor alpha chain expression on CD4(+) T cells during T helper (Th)1/Th2 differentiation. Critical downregulatory role of IL-4.

Interleukin (IL)-18 has been well characterized as a costimulatory factor for the induction of IL-12-mediated interferon (IFN)-gamma production by T helper (Th)1 cells, but also can induce IL-4 production and thus facilitate the differentiation of Th2 cells. To determine the mechanisms by which IL-18 might regulate these diametrically distinct immune responses, we have analyzed the role of cytokines in the regulation of IL-18 receptor alpha chain (IL-18Ralpha) expression. The majority of peripheral CD4(+) T cells constitutively expressed the IL-18Ralpha. Upon antigen stimulation in the presence of IL-12, marked enhancement of IL-18Ralpha expression was observed. IL-12-mediated upregulation of IL-18Ralpha required IFN-gamma. Activated CD4(+) T cells that expressed low levels of IL-18Ralpha could produce IFN-gamma when stimulated with the combination of IL-12 and IL-18, while CD4(+) cells which expressed high levels of IL-18Ralpha could respond to IL-18 alone. In contrast, T cell stimulation in the presence of IL-4 resulted in a downregulation of IL-18Ralpha expression. Both IL-4(-/)- and signal transducer and activator of transcription (Stat)6(-/)- T cells expressed higher levels of IL-18Ralpha after TCR stimulation. Furthermore, activated T cells from Stat6(-/)- mice produced more IFN-gamma in response to IL-18 than wild-type controls. Thus, positive/negative regulation of the IL-18Ralpha by the major inductive cytokines (IL-12 and IL-4) determines the capacity of IL-18 to polarize an immune response.

Cutting edge: control of CD8+ T cell activation by CD4+CD25+ immunoregulatory cells.

CD4(+)CD25(+) regulatory T cells inhibit organ-specific autoimmune diseases induced by CD4(+)CD25(-) T cells and are potent suppressors of CD4(+)CD25(-) T cell activation in vitro. We demonstrate that CD4(+)CD25(+) T cells also suppress both proliferation and IFN-gamma production by CD8(+) T cells induced either by polyclonal or Ag-specific stimuli. CD4(+)CD25(+) T cells inhibit the activation of CD8(+) responders by inhibiting both IL-2 production and up-regulation of IL-2Ralpha-chain (CD25) expression. Suppression is mediated via a T-T interaction as activated CD4(+)CD25(+) T cells suppress the responses of TCR-transgenic CD8(+) T cells stimulated with soluble peptide-MHC class I tetramers in the complete absence of APC. These results broaden the immunoregulatory role played by CD4(+)CD25(+) T cells in the prevention of autoimmune diseases, but also raise the possibility that they may hinder the induction of effector CD8(+) T cells to tumor or foreign Ags.

A T cell receptor transgenic model of severe, spontaneous organ-specific autoimmunity.

The development of mouse models of human organ-specific autoimmune diseases has been hampered by the need to immunize mice with autoantigens in potent adjuvants. Even autoantigen-specific T cell receptor transgenic models of autoimmunity have proven to be complex as the transgenic mice frequently fail to develop disease spontaneously. We have isolated a CD4(+) T cell clone (TxA23)that recognizes the gastric parietal cell antigen, H/K ATPase alpha-chain(630-641), from a mouse with autoimmune gastritis that developed after thymectomy on day 3 of life. The T cell receptor alpha and beta genes from this clone were used to generate A23 transgenic mice. All A23 transgenic animals spontaneously developed severe autoimmune gastritis, and evidence of disease was detected as early as day 10 of life. Gastritis could be transferred to immunocompromised mice with a limited number of transgenic thymocytes (10(3)), but as many as 10(7) induced only mild disease in wild-type animals. Due to the complete penetrance of spontaneous disease, identity of the auto-antigen, susceptibility to immunoregulation, and close relation to autoimmune gastritis in man, A23 transgenic mice represent a unique CD4(+) T cell-mediated disease model for understanding the multiple factors regulating organ-specific autoimmunity.

A heritable defect in IL-12 signaling in B10.Q/J mice. I. In vitro analysis.

B10.Q mice are normally susceptible to the induction of collagen-induced arthritis. We noted that one subline of B10.Q mice, B10.Q/J, was completely resistant to disease induction when immunized with collagen in CFA. B10.Q/J mice have a global defect in the generation of Th1 responses, and Ag-specific T cells derived from this strain failed to produce IFN-gamma. Because T cells from these mice could produce normal amounts of IFN-gamma when activated by IL-12/IL-18-independent stimuli, the defect appeared to be a failure to respond to IL-12. This defect extended to NK cells, which also failed to produce IFN-gamma when stimulated by IL-12. The capacity of NK cells, but not activated T cells, to produce IFN-gamma in response to IL-12 could be partially restored by IL-18. The expression of the IL-12R beta1- and beta2-chains on T cells and NK cells from B10.Q/J mice was normal. However, activated T cells from B10.Q/J mice did not signal normally through the IL-12R and manifested a defect in their capacity to phosphorylate Stat4. This defect was partial in that it could be overcome by increasing both the concentration of IL-12 and the incubation times in the Stat4 phosphorylation assays. Because Stat4 function is apparently intact in B10.Q/J mice, the defect in IL-12 signaling can be localized between the IL-12R complex and Stat4. This subtle abnormality in IL-12 responsiveness results in a profound defect in the generation of Th1 cells and the development of autoimmune disease.

A heritable defect in IL-12 signaling in B10.Q/J mice. II. Effect on acute resistance to Toxoplasma gondii and rescue by IL-18 treatment.

This study documents a defect in IL-12-dependent IFN-gamma responses in a substrain (B10.Q-H2-(q)/SgJ) of B10.Q mice that manifests as an acute susceptibility to infection by the intracellular protozoan pathogen, Toxoplasma gondii. Despite robust systemic production of IL-12, infected B10.Q/J animals fail to mount an early IFN-gamma response after parasite inoculation. Genetic experiments revealed that the host resistance and IFN-gamma production defects are determined by a single autosomal recessive locus distinct from the Stat4 gene. Nonetheless, a delayed IL-12-mediated IFN-gamma response emerges in later stages of acute infection but is unable to prevent host mortality. IL-18 administration restores, in an IL-12-dependent manner, the early IFN-gamma response and host resistance of B10.Q/J animals. These in vivo studies indicate that the partially impaired IL-12 responsiveness in B10.Q/J mice can result in defective host resistance and demonstrate a therapeutic function for IL-18 in reversing a genetically based immunodeficiency in IL-12-dependent IFN-gamma production.

Susceptibility to collagen-induced arthritis: cytokine-mediated regulation.

Collagen-induced arthritis is an animal model of inflammatory polyarthritis that is induced in susceptible strains of rats and mice by intradermal immunization with heterologous type II collagen emulsified in complete Freund's adjuvant. Previous studies have demonstrated that disease induction is highly MHC-restricted, with only mice of H-2(q) or H-2(r) haplotypes being susceptible. We have used a panel of both susceptible and resistant strains of mice in which either IFN-gamma or IL-10 signaling has been abolished by gene deletion and show that disease can be readily induced in several resistant strains of the H-2(b) and H-2(d) haplotype; susceptibility was highly dependent on IL-12. IL-4 was also shown to be crucial for disease induction in this model. These results suggest that both Th1 and Th2 cytokines may be important in the etiopathogenesis of disease and that disease susceptibility may be a function of a dysregulated cytokine environment.

Labeling cells in microtiter plates for determination of [3H]thymidine uptake.

A number of protocols in Current Protocols in Immunology use as their end-point the determination of cell proliferation by determining the incorporation of [(3)H]thymidine into cellular DNA. This appendix presents a protocol in which the radioactive label is added during the last 4 to 24 hr of the culture. A semiautomated cell harvesting apparatus is then used to lyse the cells with water and precipitate the labeled DNA on glass fiber filters. The filter pads are then dried and counted by standard liquid scintillation counting techniques in a scintillation counter.

Regulatory T cells in autoimmmunity*.

Clonal deletion of autoreactive T cells in the thymus is not the sole mechanism for the induction of tolerance to self-antigens since partial depletion of peripheral CD4(+) T cells from neonatal and adult animals results in the development of organ-specific autoimmunity. Reconstitution of these immunodeficient animals with populations of regulatory CD4(+)T cells prevents the development of autoimmunity. The lineage of regulatory CD4(+) T cells is generated in the thymus and can be distinguished from effector cells by the expression of unique membrane antigens. The target antigens for these suppressor populations and their mechanisms of action remain poorly defined. Depletion of regulatory T cells may be useful in the induction of immunity to weak antigens, such as tumor-specific antigens. Conversely, enhancement of regulatory T cell function may be a useful adjunct to the therapy of autoimmune diseases and for prevention of allograft rejection.

CpG oligonucleotides are potent adjuvants for the activation of autoreactive encephalitogenic T cells in vivo.

The mechanism of action of microbial adjuvants in promoting the differentiation of autoimmune effector cells remains to be elucidated. We demonstrate that CpG-containing oligodeoxynucleotides (ODN) can completely substitute for heat-killed mycobacteria in the priming of encephalitogenic myelin-reactive T cells in vivo. The adjuvanticity of the CpG ODN was secondary to their direct ability to induce IL-12 or to act synergistically with endogenous IL-12 to promote Th1 differentiation and encephalitogenicity. T cells primed in the absence of CpG with Ag and IFA alone appeared to be in a transitional state and had not undergone differentiation along a conventional Th pathway. Unlike Th2 cells, they expressed low levels of the IL-12R beta 2 subunit and retained the ability to differentiate into encephalitogenic effectors when reactivated in vitro under Th1-polarizing conditions. These results support the use of CpG ODN as adjuvants but also suggest that they could potentially trigger autoimmune disease in a susceptible individual.

The costimulatory effect of IL-18 on the induction of antigen-specific IFN-gamma production by resting T cells is IL-12 dependent and is mediated by up-regulation of the IL-12 receptor beta2 subunit.

IL-18 was originally described as a cytokine which induced IFN-gamma production by established Th1 cells in an IL-12-independent manner. However, subsequent studies demonstrated that exogenous IL-18 in the absence of IL-12 failed to drive Th1 differentiation of naive cells and induced IFN-gamma from established Th1 cells only in combination with IL-12. We have examined the role of endogenous IL-18 in controlling Th1 lineage commitment. When naive TCR-transgenic T cells were stimulated with antigen, anti-IL-18 antibodies resulted in partial inhibition of IFN-gamma production, but did not inhibit Th1 differentiation. To distinguish whether the inhibitory effect of anti-IL-18 antibodies was mediated directly by blocking IFN-gamma production or indirectly by blocking IL-12Rbeta2 up-regulation, naive T cells from IL-12 - / - mice were stimulated with anti-CD3 and IL-18. These cells failed to produce IFN-gamma, but markedly up-regulated IL-12Rbeta2 expression. We propose that the major effect of IL-18 on Th1 development is mediated by up-regulation of IL-12Rbeta2 expression, thereby enhancing IL-12-mediated signaling. The enhancement of IL-12Rbeta2 expression by IL-18 may be particularly important for the differentiation of foreign antigen- or autoantigen-specific Th1 cells when the stimulatory concentration of IL-12 in the microenvironment is just below the threshold required for Th1 development.

Cbl-b regulates the CD28 dependence of T-cell activation.

Whereas co-stimulation of the T-cell antigen receptor (TCR) and CD28 triggers T-cell activation, stimulation of the TCR alone may result in an anergic state or T-cell deletion, both possible mechanisms of tolerance induction. Here we show that T cells that are deficient in the adaptor molecule Cbl-b (ref. 3) do not require CD28 engagement for interleukin-2 production, and that the Cbl-b-null mutation (Cbl-b(-/-)) fully restores T-cell-dependent antibody responses in CD28-/- mice. The main TCR signalling pathways, such as tyrosine kinases Zap-70 and Lck, Ras/mitogen-activated kinases, phospholipase Cgamma-1 and Ca2+ mobilization, were not affected in Cbl-b(-/-) T cells. In contrast, the activation of Vav, a guanine nucleotide exchange factor for Rac1/Rho/CDC42, was significantly enhanced. Our findings indicate that Cbl-b may influence the CD28 dependence of T-cell activation by selectively suppressing TCR-mediated Vav activation. Mice deficient in Cbl-b are highly susceptible to experimental autoimmune encephalomyelitis, suggesting that the dysregulation of signalling pathways modulated by Cbl-b may also contribute to human autoimmune diseases such as multiple sclerosis.