Intestinal CX3C chemokine receptor 1(high) (CX3CR1(high)) myeloid cells prevent T-cell-dependent colitis.

Adequate activation of CD4(+) T lymphocytes is essential for host defense against invading pathogens; however, exaggerated activity of effector CD4(+) T cells induces tissue damage, leading to inflammatory disorders such as inflammatory bowel diseases. Several unique subsets of intestinal innate immune cells have been identified. However, the direct involvement of innate immune cell subsets in the suppression of T-cell-dependent intestinal inflammation is poorly understood. Here, we report that intestinal CX(3)C chemokine receptor 1(high) (CX(3)CR1(high)) CD11b(+) CD11c(+) cells are responsible for prevention of intestinal inflammation through inhibition of T-cell responses. These cells inhibit CD4(+) T-cell proliferation in a cell contact-dependent manner and prevent T-cell-dependent colitis. The suppressive activity is abrogated in the absence of the IL-10/Stat3 pathway. These cells inhibit T-cell proliferation by two steps. Initially, CX(3)CR1(high) CD11b(+) CD11c(+) cells preferentially interact with T cells through highly expressed intercellular adhesion molecule-1/vascular cell adhesion molecule-1; then, they fail to activate T cells because of defective expression of CD80/CD86. The IL-10/Stat3 pathway mediates the reduction of CD80/CD86 expression. Transfer of wild-type CX(3)CR1(high) CD11b(+) CD11c(+) cells prevents development of colitis in myeloid-specific Stat3-deficient mice. Thus, these cells are regulatory myeloid cells that are responsible for maintaining intestinal homeostasis.

Local microbleeding facilitates IL-6- and IL-17-dependent arthritis in the absence of tissue antigen recognition by activated T cells.

Cognate antigen recognition by CD4(+) T cells is thought to contribute to the tissue specificity of various autoimmune diseases, particularly those associated with class II MHC alleles. However, we show that localized class II MHC-dependent arthritis in F759 mice depends on local events that result in the accumulation of activated CD4(+) T cells in the absence of cognate antigen recognition. In this model, transfer of in vitro polarized Th17 cells combined with the induction of experimental microbleeding resulted in CCL20 production, the accumulation of T cells in the joints, and local production of IL-6. Disease induction required IL-17A production by transferred T cells, IL-6 and CCL20 expression, and STAT3 signaling in type I collagen-expressing cells. Our data suggest a model in which the development of autoimmune disease in F759 mice depends on four events: CD4(+) T cell activation regardless of antigen specificity, local events that induce T cell accumulation, enhanced sensitivity to T cell-derived cytokines in the tissue, and activation of IL-6 signaling in the tissue. This model provides a possible explanation for why tissue-specific antigens recognized by activated CD4(+) T cells have not been identified in many autoimmune diseases, especially those associated with class II MHC molecules.

Hepatic interleukin-7 expression regulates T cell responses.

Systemic cytokine activity in response to Toll-like receptor (TLR) signaling induces the expression of various proteins in the liver after infections. Here we show that Interleukin-7 (IL-7), the production of which was thought to occur at a constant rate in vivo, was a hepatically expressed protein that directly controled T cell responses. Depletion of IL-7 expression in the liver abrogated several TLR-mediated T cell events, including enhanced CD4+ T cell and CD8+ T cell survival, augmented CD8+ T cell cytotoxic activity, and the development of experimental autoimmune encephalitis, a Th17 cell-mediated autoimmune disease. Thus, T cell responses are regulated by hepatocyte-derived IL-7, which is expressed in response to TLR signaling in vivo. We suggested that TLR-induced IL-7 expression in the liver, which is an acute-phase response, may be a good diagnostic and therapeutic target for efficient vaccine developments and for conditions characterized by TLR-mediated T cell dysregulation, including autoimmune diseases.

IL-2 in vivo activities and antitumor efficacy enhanced by an anti-IL-2 mAb.

IL-2 is a potent immunostimulant and has been tested for clinical use, including in immunotherapy for cancers and HIV infection. Here we show that a widely used neutralizing anti-murine IL-2 mAb (S4B6) exhibits unexpected activities that enhance the treatment effects of IL-2 in vivo. Coinjection of the anti-IL-2 mAb with a plasmid carrying murine IL-2 cDNA significantly increased the serum IL-2 levels and induced a substantial increase in the division of CD8+ T and NK1.1(high) cells in vivo. Injection of the mAb premixed with recombinant murine IL-2 showed the same enhanced effect. A 5-day treatment with the anti-IL-2 mAb alone gradually increased the CD44(high)CD8+ population, and the increased population was maintained for >300 days, suggesting that the mAb can gradually maintain and potentially enhance the bioactivity of endogenous IL-2 for extended periods. Furthermore, combined treatment with the anti-IL-2 mAb plus the IL-2 plasmid markedly enhanced Ag-specific CTL activity in vivo and partially protected mice from tumor metastasis to the lungs, compared with the anti-IL-2 mAb or IL-2 plasmid alone. These results demonstrated IL-2-enhancing effects of the anti-IL-2 mAb in vivo and suggest that combining a neutralizing anti-IL-2 Ab with IL-2 gene delivery might be used effectively to enhance IL-2 functions in clinical applications.

Evidence of a novel IL-2/15R beta-targeted cytokine involved in homeostatic proliferation of memory CD8+ T cells.

The homeostasis of memory CD8+ T cells is regulated by cytokines. IL-15 is shown to promote the proliferation of memory CD8+ T cells, while IL-2 suppresses their division in vivo. This inhibitory effect of IL-2 appears to occur indirectly, through other cell populations including CD25+CD4+ T cells; however, the details of this mechanism remain unclear. In this study, we show that 1) both Ag-experienced and memory phenotype CD8+ T cells divided after the depletion of IL-2 in vivo; 2) this division occurred normally and CD44(high)IL-2/15Rbeta(high) CD8+ T cells generated after IL-2 depletion in IL-15 knockout (KO) and in IL-7-depleted IL-15 KO mice; 3) surprisingly, the blockade of IL-2/15Rbeta signaling in IL-2-depleted IL-15 KO mice completely abolished the division of memory CD8+ T cells, although the only cytokines known to act through IL-2/15Rbeta are IL-2 and IL-15; and 4) the expression of IL-2/15Rbeta molecules on memory CD8+ T cells was required for their division induced by IL-2 depletion. These results demonstrate that the depletion of IL-2 in vivo induced memory CD8+ T cell division by an IL-15-independent but by an IL-2/15Rbeta-dependent mechanism, suggesting the existence of a novel IL-2/15Rbeta-utilizing cytokine that acts directly on memory CD8+ T cells to promote cell division.