Cytokines of the interleukin-1 (IL-1) family, such as IL-1 alpha/beta and IL-18, have important functions in host defense, immune regulation, and inflammation. Insight into their biological functions has led to novel therapeutic approaches to treat human inflammatory diseases. Within the IL-1 family, IL-1 alpha/beta, IL-1Ra, and IL-18 have been matched to their respective receptor complexes and have been shown to have distinct biological functions. The most prominent orphan IL-1 receptor is ST 2. This receptor has been described as a negative regulator of Toll-like receptor-IL-1 receptor signaling, but it also functions as an important effector molecule of T helper type 2 responses. We report a member of the IL-1 family, IL-33, which mediates its biological effects via IL-1 receptor ST 2, activates NF-kappaB and MAP kinases, and drives production of T(H)2-associated cytokines from in vitro polarized T(H)2 cells. In vivo, IL-33 induces the expression of IL-4, IL-5, and IL-13 and leads to severe pathological changes in mucosal organs.

Interleukin (IL)-23 is a heterodimeric cytokine composed of a unique p19 subunit, and a common p40 subunit shared with IL-12. IL-12 is important for the development of T helper (Th)1 cells that are essential for host defense and tumor suppression. In contrast, IL-23 does not promote the development of interferon-γ–producing Th1 cells, but is one of the essential factors required for the expansion of a pathogenic CD4+ T cell population, which is characterized by the production of IL-17, IL-17F, IL-6, and tumor necrosis factor. Gene expression analysis of IL-23–driven autoreactive T cells identified a unique expression pattern of proinflammatory cytokines and other novel factors, distinguishing them from IL-12–driven T cells. Using passive transfer studies, we confirm that these IL-23–dependent CD4+ T cells are highly pathogenic and essential for the establishment of organ-specific inflammation associated with central nervous system autoimmunity.

Interleukin-12 (IL-12) is a heterodimeric molecule composed of p35 and p40 subunits. Analyses in vitro have defined IL-12 as an important factor for the differentiation of naive T cells into T-helper type 1 CD4+ lymphocytes secreting interferon-gamma (refs 1, 2). Similarly, numerous studies have concluded that IL-12 is essential for T-cell-dependent immune and inflammatory responses in vivo, primarily through the use of IL-12 p40 gene-targeted mice and neutralizing antibodies against p40. The cytokine IL-23, which comprises the p40 subunit of IL-12 but a different p19 subunit, is produced predominantly by macrophages and dendritic cells, and shows activity on memory T cells. Evidence from studies of IL-23 receptor expression and IL-23 overexpression in transgenic mice suggest, however, that IL-23 may also affect macrophage function directly. Here we show, by using gene-targeted mice lacking only IL-23 and cytokine replacement studies, that the perceived central role for IL-12 in autoimmune inflammation, specifically in the brain, has been misinterpreted and that IL-23, and not IL-12, is the critical factor in this response. In addition, we show that IL-23, unlike IL-12, acts more broadly as an end-stage effector cytokine through direct actions on macrophages.

A novel sequence discovered in a computational screen appears distantly related to the p35 subunit of IL-12. This factor, which we term p19, shows no biological activity by itself; instead, it combines with the p40 subunit of IL-12 to form a novel, biologically active, composite cytokine, which we term IL-23. Activated dendritic cells secrete detectable levels of this complex. IL-23 binds to IL-12R beta 1 but fails to engage IL-12R beta 2; nonetheless, IL-23 activates Stat4 in PHA blast T cells. IL-23 induces strong proliferation of mouse memory (CD4(+)CD45Rb(low)) T cells, a unique activity of IL-23 as IL-12 has no effect on this cell population. Similar to IL-12, human IL-23 stimulates IFN-gamma production and proliferation in PHA blast T cells, as well as in CD45RO (memory) T cells.

Whether epithelial cells play a role in triggering the immune cascade leading to T helper 2 (T H 2)-type allergic inflammation is not known.We show here that human thymic stromal lymphopoietin (TSLP) potently activated CD11c + dendritic cells (DCs) and induced production of the T H 2-attracting chemokines TARC (thymus and activation-regulated chemokine; also known as CCL17) and MDC (macrophage-derived chemokine; CCL22).TSLP-activated DCs primed naïve T H cells to produce the proallergic cytokines interleukin 4 (IL-4), IL-5, IL-13 and tumor necrosis factor-α, while downregulating IL-10 and interferon-γ. TSLP was highly expressed by epithelial cells, especially keratinocytes from patients with atopic dermatitis.TSLP expression was associated with Langerhans cell migration and activation in situ.These findings shed new light on the function of human TSLP and the role played by epithelial cells and DCs in initiating allergic inflammation. Human epithelial cells trigger dendritic cell-mediated allergic inflammation by producing TSLPAbout 20% of the population in Western countries suffers from allergic diseases, which include asthma, allergic rhinitis, atopic dermatitis and food allergy 1 . Allergic inflammation is the result of a complex immunological cascade that leads to dysregulated production of T helper type 2 (TH2)-derived cytokines such as interleukin 4 (IL-4), IL-5 and IL-13 2-4 , which trigger immunoglobulin E (IgE) production, eosinophilia and mucus production [5][6][7] . Dendritic cells (DCs), which are professional antigen-presenting cells 8 , play an important role in the pathogenesis of allergic diseases 9-11 . However, the initial signal that primes DCs to induce T cells to produce proallergic TH2 cytokines is unknown. Epithelial cells are located at the sites of allergen entry into the body and interact closely with DCs in situ. However, it is not known whether DCs play a role in triggering the allergic immune cascade. Although skin keratinocytes and mucosal epithelial cells produce proinflammatory cytokines such as IL-1, IL-6, IL-8, granulocyte-macrophage colony-stimulating factor (GM-CSF) and tumor necrosis factor-α (TNF-α) after activation 12 , none of these cytokines explain the mechanism that underlies the induction of allergic inflammation. Thymic stromal lymphopoietin (TSLP) is an IL-7-like cytokine, cloned from a murine thymic stromal cell line 13 . The TLSP receptor is a heterodimer that consists of the IL-7 receptor α chain (IL-7Rα) and a common γ-like receptor chain called TSLP receptor (TSLPR) [14][15][16][17] . Mouse TSLP supports murine early B and T cell developments 18,19 and does not appear to have any biological effects on murine DCs (unpublished data). In contrast, human TSLP activates CD11c + DCs, but does not appear to have any direct biological effects on B cells, T cells, NK cells, neutrophils or mast cells 17 . This is in accordance with the coexpression of IL-7Rα chain and TSLPR mRNA in CD11c + DCs, but not in other cell types. We show here that human TSLP potently activated ...