Murine chronic graft-versus-host-disease (cGvHD) induced by injection of parental lymphocytes into F1 hybrids results in a disease similar to systemic lupus erythematosus. Here, we have used DBA/2 T cell injection into (C57BL/6 × DBA/2)F1 (BDF1) mice as a model system to test the prophylactic and therapeutic effects of interleukin-2 (IL-2)/anti-IL-2 immune complexes on the course of cGvHD. Our findings demonstrate that pretreatment with Treg inducing JES6/IL-2 complexes render BDF1 mice largely resistant to induction of cGvHD, whereas pretreatment with CD8+ T cell/NK cell inducing S4B6/IL-2 complexes results in a more severe cGvHD. In contrast, treatment with JES6/IL-2 complexes 4 weeks after induction had no beneficial effect on disease symptoms. However, similar treatment with S4B6/IL-2 complexes led to a significant amelioration of the disease. This therapeutic effect seems to be mediated by donor CD8+ T cells. The fact that a much stronger cGvHD is induced in BDF1 mice depleted of donor CD8+ T cells strongly supports this conclusion. The contrasting effects of the two different IL-2 complexes are likely due to different mechanisms.

Development of a self-tolerant T-cell receptor (TCR) repertoire with the potential to recognize the universe of infectious agents depends on proper regulation of TCR signalling. The repertoire is whittled down during T-cell development in the thymus by the ability of quasi-randomly generated TCRs to interact with self-peptides presented by major histocompatibility complex (MHC) proteins. Low-affinity TCR interactions with self-MHC proteins generate weak signals that initiate 'positive selection', causing maturation of CD4- or CD8αβ-expressing 'single-positive' thymocytes from CD4(+)CD8αβ(+) 'double-positive' precursors. These develop into mature naive T cells of the secondary lymphoid organs. TCR interaction with high-affinity agonist self-ligands results in 'negative selection' by activation-induced apoptosis or 'agonist selection' of functionally differentiated self-antigen-experienced T cells. Here we show that positive selection is enabled by the ability of the T-cell-specific protein Themis to specifically attenuate TCR signal strength via SHP1 recruitment and activation in response to low- but not high-affinity TCR engagement. Themis acts as an analog-to-digital converter translating graded TCR affinity into clear-cut selection outcome. By dampening mild TCR signals Themis increases the affinity threshold for activation, enabling positive selection of T cells with a naive phenotype in response to low-affinity self-antigens.

The zinc-finger PR domain transcriptional repressor Blimp-1/Prdm1 plays essential roles in primordial germ cell specification, placental, heart, and forelimb development, plasma cell differentiation, and T-cell homeostasis. The present experiments demonstrate that the mouse Prdm1 gene has three alternative promoter regions. All three alternative first exons splice directly to exon 3, containing the translational start codon. To examine possible cell-type-specific functional activities in vivo, we generated targeted deletions that selectively eliminate two of these transcriptional start sites. Remarkably, mice lacking the previously described first exon develop normally and are fertile. However, this region contains NF-kappaB binding sites, and as shown here, NF-kappaB signaling is required for Prdm1 induction. Thus, mutant B cells fail to express Prdm1 in response to lipopolysaccharide stimulation and lack the ability to become antibody-secreting cells. An alternative distal promoter located approximately 70 kb upstream, giving rise to transcripts strongly expressed in the yolk sac, is dispensable. Thus, the deletion of exon 1B has no noticeable effect on expression levels in the embryo or adult tissues. Collectively, these experiments provide insight into the organization of the Prdm1 gene and demonstrate that NF-kappaB is a key mediator of Prdm1 expression.

The mechanism by which CD1d-restricted Valpha14 natural killer T (NKT) cells participate in transplant tolerance has yet to be completely clarified. Recently, we showed that repeated activation of NKT cells by their specific glycolipid ligand, alpha-galactosylceramide, leads to a change in function to an immune regulatory role with IL-10 production. Moreover, these cells were shown to be able to induce regulatory dendritic cells (DCs). In this study, we showed that NKT cells from transplant tolerant recipients of cardiac allograft produced higher levels of IL-10, which is required for the maintenance of tolerance; this was proved by adoptive transfer experiments. In addition, DCs from wild-type (WT) tolerant recipients but not NKT cell-deficient recipients showed a higher IL-10-producing profile, a more immature phenotype, and tolerogenic capability. CD4 T cells from WT tolerant recipients but not NKT cell-deficient recipients also produced higher levels of IL-10 upon alloantigen stimulation and showed lower proliferative activity that was reversed by blocking the IL-10 receptor. These data indicate the existence of IL-10-dependent immune regulatory interplay among NKT cells, DCs, and CD4 T cells, even in the absence of artificial stimulation of NKT cells with synthetic glicolipids, which is required for the maintenance of transplant tolerance.

The suppressor of cytokine signaling-1 (SOCS1) is a potent negative regulator of various cytokines and it has been implicated in the regulation of immune responses. However, the role of SOCS1 in inflammatory bowel diseases (IBDs) has not been clarified. To determine the role of SOCS1 in colitis, we generated SOCS1/T-cell receptor alpha (TCRalpha) double knockout (DKO) mice.
The depletion of interferon gamma (IFNgamma) and IL-4 was achieved by crossing the DKO mice with IFNgamma knockout (KO) mice and by the administration of anti-IL-4 antibody, respectively. The activation of cytokine-induced transcription factors was determined by Western blotting with phosphorylation-specific antibodies, and the induction of inflammatory factors was measured by reverse-transcription polymerase chain reaction.
Much more severe colitis developed in 100% of the DKO mice within 9 weeks of age than in TCRalpha-KO mice. Although the proportion and the activation status of CD4(+) TCRalpha(-)beta(+) T cells in DKO mice were similar to those in TCRalpha-KO mice, signal transducer and activator of transcription 1, nuclear factor kappaB, and their target genes were hyperactivated in infiltrated mononuclear cells and colonic epithelial cells in DKO mice. Cytokine-depletion experiments showed that exacerbated colitis in the DKO mice was dependent on both IFNgamma and IL-4. SOCS1-deficient cells were hypersensitive to IFNgamma, IL-4, and lipopolysaccharides, depending on the target genes.
SOCS1 plays an important role in preventing murine colitis by restricting the cytokine signals. SOCS1/TCRalpha DKO mice could be a useful model for investigating human IBD.