IntroductionCytokines of the interleukin (IL)-1 family are major proinflammatory and immunoregulatory mediators that act through receptors of the Toll-like/IL-1-receptor (TLR/IL-1R) superfamily. Due to homologous intracellular Toll/interleukin-1 receptor (TIR) domains, IL-1 family members and TLR-ligands activate very similar signaling pathways leading to NF-B-and MAPKactivation. 1 IL-1␣ and IL-1␤, the prototypic family members, are generated in response to exogenous and endogenous danger signals and act as chief inflammatory mediators in many inflammatory conditions. 2 Recent studies indicate that IL-1 may also participate in inflammatory pathologies and auto-immune diseases involving Th17-type T-helper cells. [3][4][5] By contrast, IL-18 is best known for its role in Th1-type immune responses because it strongly amplifies IFN-␥ production in natural killer (NK) cells and Th1 cells in synergy with However, several lines of evidence mainly derived from mouse models indicate that IL-18 can also play a role in allergic diseases and defense against helminths. 6,7 For example, in the absence of IFN-␥ signaling, IL-18 increases immunoglobulin E (IgE) levels and promotes a Th2-type pathology. 8 It has been suggested that this is due to the antigen-independent action of IL-18 on cells of the "innate allergic response," basophils and mast cells. 7 Bone marrow-derived c-Kit Ϫ /Fc⑀RI ϩ mouse "basophil-like" cells express IL-18 receptors (IL-18R), and IL-18 induces IL-4 and IL-13 expression in an antigen-independent manner as efficiently as In the human system, IL-18 primes basophilic KU812 cells for enhanced leukotriene C 4 (LTC 4 ) production. 9 Furthermore, a recent screen of novel CD antigens revealed that blood basophils express IL-18R and IL-18R-accessory protein (IL-18Rap), 10 indicating that IL-18 may also act on human basophils.A soluble form of an IL-1R family member ST2 (sST2; also called T1) has been cloned many years ago. sST2 is formed by many cells and increased sST2 levels are found in inflammatory conditions, including allergic asthma. [11][12][13] The expression of transmembrane ST2-receptor (ST2L), however, is largely restricted to cells of hematopoietic origin. ST2L is expressed by mouse bone marrow-derived mast cells (BMMCs) and is a stable marker of mouse, but not human, Th2-lymphocytes. [14][15][16][17] In the absence of a known ligand, the biologic roles of ST2 have been extensively studied in several mouse models using ST2-antibodies, sST2-constructs, and ST2-KO-mice. 14,18 Although the interpretations were sometimes conflicting, most studies indicate an important contribution of ST2 in Th2-type immune responses and allergic inflammation. The biology of ST2 is further complicated by a possible direct antiinflammatory action of sST2, and by the fact that the TIR domain of ST2L appears to be a negative regulator of 20 Research on ST2 strongly gained momentum by the recent discovery of its ligand, the novel IL-1 family member IL-33. 21 Like IL-1␣, the human IL-33 precursor (proIL-33) is a nuclear pr...

Immunoglobulin E (IgE) is central to the induction of allergic diseases through its binding to the high-affinity receptor (Fc epsilon R1) on mast cells and basophils. Crosslinking by allergens of the bound IgE leads to the release of various inflammatory mediators. IgE production by B cells requires a physical interaction with T cells, involving a number of surface adhesion molecules, as well as the soluble factors interleukin-4 (IL-4) and IL-13 (ref. 5) produced by T cells, basophils and mast cells. Here we report that, in the presence of IL-4, mast and basophilic cell lines can provide the cell contact signals that are required for IgE synthesis. The human cell lines HMC-1 (mast) and KU812 (basophilic) both express the ligand for CD40 (CD40L) which is shown to be responsible for the IgE production. Moreover, freshly isolated purified human lung mast cells and blood basophils are also shown to express CD40L and to induce IgE production. This evidence suggests that mast cells and basophils may therefore play a key role in allergy not only by producing inflammatory mediators, but also by directly regulating IgE production independently of T cells.

Sllmmsr~The cellular infiltrates of certain inflammatory processes found in parasitic infection or in allergic diseases consist predominantly of eosinophilic granulocytes, often in association with activated T cells. This suggests the existence of chemotactic agonists specific for eosinophils and lymphocyte subsets devoid of neutrophil-activating properties. We therefore examined four members of the intercrine/chemokine superfamily of cytokines (monocyte chemotactic peptide 1 [MCP-1], RANTES, macrophage inflammatory protein 1ix [MIP-ltx], and MIP-1/3), which do not activate neutrophils, for their ability to affect different eosinophil effector functions. R.ANTES strongly attracted normal human eosinophils by a chemotactic rather than a chemokinetic mechanism with a similar efficacy as the most potent chemotactic myeloid cell agonist, C5a. MIP-ltx also induced eosinophil migration, however, with lower efficacy. RANTES and MIP-lo~ induced eosinophil cationic protein release in cytochalasin B-treated eosinophils, but did not promote leukotriene C4 formation by eosinophils, even after preincubation with interleukin 3 (IL-3), in contrast to other chemotactic agonists such as C5a and formyl-methionyl-lencyl-phenylalanine (FMLP). RANTES, but not MIP-ltx, induced a biphasic chemiluminescence response, however, of lower magnitude than C5a. RANTES and MIP-lo~ both promoted identical transient changes in intracellular free calcium concentration ([Ca2+]i), with kinetics similar to those induced by chemotactic peptides known to interact with G protein-coupled receptors. No cross-desensitization towards other peptide agonists (e.g., C5a, IL-8, FMLP) was observed, suggesting the presence of specific receptors. Despite its weaker eosinophil-activating properties, MIP-lol was at least 10 times more potent on a molar basis than R.ANTES at inducing [Ca 2+ ]i changes. Interestingly, RANTES deactivated the MIP-lcz-induced [Ca2+]i changes, while the R.ANTES response was preserved after MIP-lcz stimulation. MCP-1, a potent monocyte chemoattractant and basophil agonist, as well as MIP-1/3, a peptide with pronounced homology to MIP-lo~, did not activate the eosinophil functions tested. Our results indicate that R.ANTES and MIP-ltx are crucial mediators of inflammatory processes in which eosinophils predominate.

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A novel human CC chemokine consisting of 78 amino acids and having a molecular mass of 8,778.3 daltons (VVIPSPCCMF FVSKRIPENR VVSYQLSSRS TCLKAGVIFT TKKGQQ SCGD PKQEWVQRYM KNLDAKQKKA SPRARAVA) was isolated together with three minor COOH-terminally truncated variants with 73, 75, and 76 residues. The new chemokine was termed eotaxin-2 because it is functionally very similar to eotaxin. In terms of structure, however, eotaxin and eotaxin-2 are rather distant, they share only 39% identical amino acids and differ almost completely in the NH2-terminal region. Eotaxin-2 induced chemotaxis of eosinophils as well as basophils, with a typically bimodal concentration dependence, and the release of histamine and leukotriene C4 from basophils that had been primed with IL-3. In all assays, eotaxin-2 had the same efficacy as eotaxin, but was somewhat less potent. The migration and the release responses were abrogated in the presence of a monoclonal antibody that selectively blocks the eotaxin receptor, CCR3, indicating that eotaxin-2, like eotaxin, acts exclusively via CCR3. Receptor usage was also studied in desensitization experiments by measuring [Ca2+]i changes in eosinophils. Complete cross-desensitization was observed between eotaxin-2, eotaxin and MCP-4 confirming activation via CCR3. No Ca2+ mobilization was obtained in neutrophils, monocytes and lymphocytes, in agreement with the lack of chemotactic responsiveness. Intradermal injection of eotaxin-2 in a rhesus monkey (100 or 1,000 pmol per site) induced a marked local infiltration of eosinophils, which was most pronounced in the vicinity of postcapillary venules and was comparable to the effect of eotaxin.