Regulation of Foxp3+ inducible regulatory T cell stability by SOCS2.

Suppressor of cytokine signaling (SOCS) proteins are key regulators of CD4(+) T cell differentiation, and in particular, we have recently shown that SOCS2 inhibits the development of Th2 cells and allergic immune responses. Interestingly, transcriptome analyses have identified SOCS2 as being preferentially expressed in both natural regulatory T cells (Tregs) and inducible Tregs (iTregs); however, the role of SOCS2 in Foxp3(+) Treg function or development has not been fully elucidated. In this study, we show that despite having no effect on natural Treg development or function, SOCS2 is highly expressed in iTregs and required for the stable expression of Foxp3 in iTregs in vitro and in vivo. Indeed, SOCS2-deficient CD4(+) T cells upregulated Foxp3 following in vitro TGF-ß stimulation, but failed to maintain stable expression of Foxp3. Moreover, in vivo generation of iTregs following OVA feeding was impaired in the absence of SOCS2 and could be rescued in the presence of IL-4 neutralizing Ab. Following IL-4 stimulation, SOCS2-deficient Foxp3(+) iTregs secreted elevated IFN-γ and IL-13 levels and displayed enhanced STAT6 phosphorylation. Therefore, we propose that SOCS2 regulates iTreg stability by downregulating IL-4 signaling. Moreover, SOCS2 is essential to maintain the anti-inflammatory phenotype of iTregs by preventing the secretion of proinflammatory cytokines. Collectively, these results suggest that SOCS2 may prevent IL-4-induced Foxp3(+) iTreg instability. Foxp3(+) iTregs are key regulators of immune responses at mucosal surfaces; therefore, this dual role of SOCS2 in both Th2 and Foxp3(+) iTregs reinforces SOCS2 as a potential therapeutic target for Th2-biased diseases.

Siglec-E is up-regulated and phosphorylated following lipopolysaccharide stimulation in order to limit TLR-driven cytokine production.

Although production of cytokines by TLR is essential for viral and bacterial clearance, overproduction can be detrimental, thus controlling these responses is essential. CD33-related sialic acid binding Ig-like lectin receptors (Siglecs) have been implicated in the control of leukocyte responses. In this study, we report that murine Siglec-E is induced by TLRs in a MyD88-specific manner, is tyrosine phosphorylated following LPS stimulation, and negatively regulates TLR responses. Specifically, we demonstrate the Siglec-E expression inhibits TLR-induced NF-kappaB and more importantly, the induction of the antiviral cytokines IFN-beta and RANTES. Siglec-E mediates its inhibitory effects on TIR domain containing adaptor inducing IFN-beta (TRIF)-dependent cytokine production via recruitment of the tyrosine [corrected] phosphatase SHP2 and subsequent inhibition of TBK1 activity as evidenced by enhanced TBK1 phosphorylation in cells following knockdown of Siglec-E expression. Taken together, our results demonstrate a novel role for Siglec-E in controlling the antiviral response to TLRs and thus helping to maintain a healthy cytokine balance following infection.

CCL11 blocks IL-4 and GM-CSF signaling in hematopoietic cells and hinders dendritic cell differentiation via suppressor of cytokine signaling expression.

The chemokine eotaxin/CCL11 is an important mediator of leukocyte migration, but its effect on inflammatory cytokine signaling has not been explored. In this study, we find that CCL11 induces suppressor of cytokine signaling (SOCS)1 and SOCS3 expression in murine macrophages, human monocytes, and dendritic cells (DCs). We also discover that CCL11 inhibits GM-CSF-mediated STAT5 activation and IL-4-induced STAT6 activation in a range of hematopoietic cells. This blockade of cytokine signaling by CCL11 results in reduced differentiation and endocytic ability of DCs, implicating CCL11-induced SOCS as mediators of chemotactic inflammatory control. These findings demonstrate cross-talk between chemokine and cytokine responses, suggesting that myeloid cells tracking to the inflammatory site do not differentiate in the presence of this chemokine, revealing another role for SOCS in inflammatory regulation.

Tubulitis in renal allograft rejection: role of transforming growth factor-beta and interleukin-15 in development and maintenance of CD103+ intraepithelial T cells.

BACKGROUND: Renal tubules normally show no lymphocyte infiltration, but tubulitis is a feature of renal allograft rejection with many intratubular T cells expressing CD8 and CD103 (the alphaEbeta7 integrin). We investigated the development and maintenance of allospecific CD103 T cells within the tubular microenvironment. METHODS: Mixed lymphocyte cultures were supplemented with transforming growth factor (TGF)-beta1 to model the expression and function of CD103 observed in situ on intratubular lymphocytes. Immunocytochemical techniques were used to identify cells coexpressing CD8 and interleukin (IL)-15Ralpha, to enumerate proliferating intratubular T cells, and to quantify IL-15 expression within the tubules of control and rejection-graded transplant biopsy specimens. These results were compared with a parallel analysis of the phenotype and proliferation of allospecific T cells expanded in vitro in the presence of TGF-beta1 and IL-15. RESULTS: TGF-beta1 only induced the expression of adhesive CD103 after at least one cycle of alloantigen-specific cell division in vitro. In the renal allograft, a similar proportion of intratubular T cells was observed to proliferate during and after acute rejection. Tubular epithelial cells expressed IL-15 constitutively, whereas intratubular CD8 T cells expressed IL-15 receptor alpha. IL-15 and TGF-beta1 synergized to promote expansion and survival of allospecific CD8 CD103 T cells in vitro, but IL-15 down-regulated perforin expression. CONCLUSIONS: These results suggest that activated, allospecific CD8 T cells are recruited to tubules during acute rejection where they encounter TGF-beta, up-regulate CD103 expression, and bind E-cadherin. A proportion of these cells proliferates and is maintained in a state of low perforin expression by the combined action of TGF-beta and IL-15.

SOCS2 regulates T helper type 2 differentiation and the generation of type 2 allergic responses.

The incidence of allergy and asthma in developed countries is on the increase and this trend looks likely to continue. CD4(+) T helper 2 (Th2) cells are major drivers of these diseases and their commitment is controlled by cytokines such as interleukin 4, which are in turn regulated by the suppressor of cytokine signaling (SOCS) proteins. We report that SOCS2(-/-) CD4(+) T cells show markedly enhanced Th2 differentiation. SOCS2(-/-) mice, as well as RAG-1(-/-) mice transferred with SOCS2(-/-) CD4(+) T cells, exhibit elevated type 2 responses after helminth antigen challenge. Moreover, in in vivo models of atopic dermatitis and allergen-induced airway inflammation, SOCS2(-/-) mice show significantly elevated IgE, eosinophilia, type 2 responses, and inflammatory pathology relative to wild-type mice. Finally, after T cell activation, markedly enhanced STAT6 and STAT5 phosphorylation is observed in SOCS2(-/-) T cells, whereas STAT3 phosphorylation is blunted. Thus, we provide the first evidence that SOCS2 plays an important role in regulating Th2 cell expansion and development of the type 2 allergic responses.

The newest interleukins: recent additions to the ever-growing cytokine family.

Cytokines play a critical role in the control of the innate and adaptive immune responses. The most recent additions to the ever-growing family of cytokines include interleukin (IL)-27, IL-28A, IL-28B, IL-29, IL-31, IL-32, and IL-33. Many of the newly identified cytokines and/or their specific receptors have been identified using bioinformatics. The coming of age of this discipline has coincided with completion of the sequencing of the human genome thus enabling the identification of new uncharacterized proteins. The latest additions to the interleukin family have shed new light on the intricacies of immune system regulation. These novel cytokines have pleiotrophic actions ranging from antiviral immunity to the regulation of Th2 immune responses. For example, the discovery of IL-27 has greatly improved our understanding of the factors regulating the polarization of the T helper cell responses and IL-31 appears to be an important regulator of Th2 responses. On the other hand, IL-28 and IL-29 are considered to be critical for mounting an efficient antiviral response and IL-32 and IL-33, which are yet to be fully characterized, are emerging as important components of the inflammatory response in allergy and autoimmunity. These new cytokine/receptor combinations may therefore serve as novel targets for the treatment and control of allergy, autoimmune diseases, and some cancers.

Immunodeficiency is a tough nut to CRAC: the importance of calcium flux in T cell activation.

Severe Combined Immunodeficiency (SCID) is a rare primary immunodeficiency disease often characterized by a block in T cell development, which may also affect the normal development of B cells and NK cells. Several different mutations are known to give rise to SCID, and multiple genes are involved. Consequently, there are several different forms of SCID, which can be classified according to the metabolic and cellular defects that impede normal lymphocyte function. The two most prevalent forms of SCID are X-linked SCID and adenosine deaminase (ADA) deficiency SCID, together accounting for approximately 70-80% of disease cases. Other genetic abnormalities associated with this syndrome range from defective T cell receptor rearrangement to non-functional signaling molecules. Recently, a new genetic defect has been described in which mutations in a key component of Ca(2+) release activated-channels (CRAC) result in T lymphocyte malfunction.

Housekeeping proteins: a preliminary study illustrating some limitations as useful references in protein expression studies.

A primary objective of many protein expression studies is to define expression patterns that can distinguish between normal and diseased states, enabling a better understanding of molecular events associated with disease development and progression and ultimately potentially finding novel markers or therapeutic targets. Exploration and confirmation of many proteins is often done using Western blotting with normalization against "housekeeping proteins", such as glyceraldehyde-3-phosphate dehydrogenase (GAPDH), beta-actin, or beta-tubulin, to correct for protein loading and factors, such as transfer efficiency. Increasingly, in studies examining gene transcript levels, it has been shown that some of the commonly used housekeeping genes may be unsuitable due to the influence of various physiological and pathological factors on their expression. This has not been examined to any great extent for proteins, however. This study examines the degree of variability of three commonly used "housekeeping" proteins (GAPDH, beta-actin, and beta-tubulin) together with class I beta-tubulin, with comparisons being made between a number of different established renal cancer cell lines, matched pairs of renal tumor and normal kidney lysates as well as nine different human tissues and highlights some of the problems encountered.