T-helper type 17 cells (T(H)17) are implicated in rodent models of immune-mediated diseases. Here we report their involvement in human uveitis and scleritis, and validate our findings in experimental autoimmune uveoretinitis (EAU), a model of uveitis. T(H)17 cells were present in human peripheral blood mononuclear cells (PBMC), and were expanded by interleukin (IL)-2 and inhibited by interferon (IFN)-gamma. Their numbers increased during active uveitis and scleritis and decreased following treatment. IL-17 was elevated in EAU and upregulated tumor necrosis factor (TNF)-alpha in retinal cells, suggesting a mechanism by which T(H)17 may contribute to ocular pathology. Furthermore, IL-27 was constitutively expressed in retinal ganglion and photoreceptor cells, was upregulated by IFN-gamma and inhibited proliferation of T(H)17. These findings suggest that T(H)1 cells may mitigate uveitis by antagonizing the T(H)17 phenotype through the IFN-gamma-mediated induction of IL-27 in target tissue. The finding that IL-2 promotes T(H)17 expansion provides explanations for the efficacy of IL-2R antibody therapy in uveitis, and suggests that antagonism of T(H)17 by IFN-gamma and/or IL-27 could be used for the treatment of chronic inflammation.

Regulatory T (Treg) cells suppress autoimmune disease, and impaired Treg cell function is associated with rheumatoid arthritis. Here we demonstrate that forkhead box P3 (FOXP3) transcriptional activity and, consequently, Treg cell suppressive function are regulated by phosphorylation at Ser418 in the C-terminal DNA-binding domain. In rheumatoid arthritis-derived Treg cells, the Ser418 site was specifically dephosphorylated by protein phosphatase 1 (PP1), whose expression and enzymatic activity were induced in the inflamed synovium by tumor necrosis factor α (TNF-α), leading to impaired Treg cell function. Moreover, TNF-α-induced Treg cell dysfunction correlated with increased numbers of interleukin-17 (IL-17)(+) and interferon-γ (IFN-γ)(+)CD4(+) T cells within the inflamed synovium in rheumatoid arthritis. Treatment with a TNF-α-specific antibody restored Treg cell function in subjects with rheumatoid arthritis, which was associated with decreased PP1 expression and increased FOXP3 phosphorylation in Treg cells. Thus, TNF-α controls the balance between Treg cells and pathogenic TH17 and TH1 cells in the synovium of individuals with rheumatoid arthritis through FOXP3 dephosphorylation.

Osmotic stress responses are critical not only to the survival of unicellular organisms but also to the normal function of the mammalian kidney. However, the extent to which cells outside the kidney rely on osmotic stress responses in vivo remains unknown. Nuclear factor of activated T cells 5 (NFAT5)͞tonicity enhancer binding protein (TonEBP), the only known osmosensitive mammalian transcription factor, is expressed most abundantly in the thymus and is induced upon lymphocyte activation. Here we report that NFAT5͞TonEBP is not only essential for normal cell proliferation under hyperosmotic conditions but also necessary for optimal adaptive immunity. Targeted deletion of exons 6 and 7 of the Nfat5 gene, which encode a critical region of the DNA-binding domain, gave rise to a complete loss of function in the homozygous state and a partial loss of function in the heterozygous state. Complete loss of function resulted in late gestational lethality. Furthermore, hypertonicity-induced NFAT5͞TonEBP transcriptional activity and hsp70.1 promoter function were completely eliminated, and cell proliferation under hyperosmotic culture conditions was markedly impaired. Partial loss of NFAT5͞TonEBP function resulted in lymphoid hypocellularity and impaired antigen-specific antibody responses in viable heterozygous animals. In addition, lymphocyte proliferation ex vivo was reduced under hypertonic, but not isotonic, culture conditions. Direct measurement of tissue osmolality further revealed lymphoid tissues to be hyperosmolar. These results indicate that lymphocyte-mediated immunity is contingent on adaptation to physiologic osmotic stress, thus providing insight into the lymphoid microenvironment and the importance of the NFAT5͞TonEBP osmotic stress response pathway in vivo.

Mammalian skeletal muscles are capable of regeneration after injury. Quiescent satellite cells are activated to reenter the cell cycle and to differentiate for repair, recapitulating features of myogenesis during embryonic development. To understand better the molecular mechanism involved in this process in vivo, we employed high density cDNA microarrays for gene expression profiling in mouse tibialis anterior muscles after a cardiotoxin injection. Among 16,267 gene elements surveyed, 3,532 elements showed at least a 2.5-fold change at one or more time points during a 14-day time course. Hierarchical cluster analysis and semiquantitative reverse transcription-PCR showed induction of genes important for cell cycle control and DNA replication during the early phase of muscle regeneration. Subsequently, genes for myogenic regulatory factors, a group of imprinted genes and genes with functions to inhibit cell cycle progression and promote myogenic differentiation, were induced when myogenic stem cells started to differentiate. Induction of a majority of these genes, including E2f1 and E2f2, was abolished in muscles lacking satellite cell activity after gamma radiation. Regeneration was severely compromised in E2f1 null mice but not affected in E2f2 null mice. This study identifies novel genes potentially important for muscle regeneration and reveals highly coordinated myogenic cell proliferation and differentiation programs in adult skeletal muscle regeneration in vivo.Skeletal muscles are damaged and repaired repeatedly throughout life. Muscle regeneration maintains locomotor function during aging and delays the appearance of clinical symptoms in neuromuscular diseases, such as Duchenne muscular dystrophy (1, 2). This capacity for tissue repair is conferred by satellite cells located between the basal lamina and the sarcolemma of mature myofibers (3, 4). Upon injury, satellite cells reenter the cell cycle, proliferate, and then exit the cell cycle either to renew the quiescent satellite cell pool or to differentiate into mature myofibers (5). Understanding the molecular mechanism by which satellite cell activity is regulated could promote development of novel countermeasures to enhance muscle performance that is compromised by diseases or aging.Both the cell proliferation and differentiation programs are essential for myogenesis. Mammalian cells escape from quiescence (G 0 ) and enter the cell cycle by activating the Cdk 1 /Rb/ E2f signaling pathway (6, 7). In general, mitogen stimulation induces expression and assembly of the G 1 cyclin-dependent kinases (Cdks) (8, 9). Activation of Cdks causes phosphorylation of the retinoblastoma protein (Rb) (10, 11), leading to increased activities of a subset of E2f transcription factors (E2fs) (12) and up-regulation of a variety of E2f-responsive genes encoding proteins directly involved in DNA replication and cell cycle progression (13,14). On the other hand, myogenic differentiation is controlled by interactions of a network of myogenic transcription factors (15). Studies ...