Thymic stromal lymphopoietin is released by human epithelial cells in response to microbes, trauma, or inflammation and potently activates mast cells.

Compelling evidence suggests that the epithelial cell-derived cytokine thymic stromal lymphopoietin (TSLP) may initiate asthma or atopic dermatitis through a dendritic cell-mediated T helper (Th)2 response. Here, we describe how TSLP might initiate and aggravate allergic inflammation in the absence of T lymphocytes and immunoglobulin E antibodies via the innate immune system. We show that TSLP, synergistically with interleukin 1 and tumor necrosis factor, stimulates the production of high levels of Th2 cytokines by human mast cells (MCs). We next report that TSLP is released by primary epithelial cells in response to certain microbial products, physical injury, or inflammatory cytokines. Direct epithelial cell-mediated, TSLP-dependent activation of MCs may play a central role in "intrinsic" forms of atopic diseases and explain the aggravating role of infection and scratching in these diseases.

Identification of functional roles for both IL-17RB and IL-17RA in mediating IL-25-induced activities.

IL-25 (IL-17E) is a unique IL-17 family ligand that promotes Th2-skewed inflammatory responses. Intranasal administration of IL-25 into naive mice induces pulmonary inflammation similar to that seen in patients with allergic asthma, including increases in bronchoalveolar lavage fluid eosinophils, bronchoalveolar lavage fluid IL-5 and IL-13 concentrations, goblet cell hyperplasia, and increased airway hyperresponsiveness. IL-25 has been reported to bind and signal through IL-17RB (IL-17BR, IL-17Rh1). It has been demonstrated recently that IL-17A signals through a heteromeric receptor composed of IL-17RA and IL-17RC. We sought to determine whether other IL-17 family ligands also utilize heteromeric receptor complexes. The required receptor subunits for IL-25 biological activities were investigated in vitro and in vivo using a combination of knockout (KO) mice and antagonistic Abs. Unlike wild-type mice, cultured splenocytes from either IL-17RB KO or IL-17RA KO mice did not produce IL-5 or IL-13 in response to IL-25 stimulation, and both IL-17RB KO and IL-17RA KO mice did not respond to intranasal administration of IL-25. Furthermore, treatment with antagonistic mAbs to either IL-17RB or IL-17RA completely blocked IL-25-induced pulmonary inflammation and airway hyperresponsiveness in naive BALB/c mice, similar to the effects of an antagonistic Ab to IL-25. Finally, a blocking Ab to human IL-17RA prevented IL-25 activity in a primary human cell-based assay. These data demonstrate for the first time that IL-25-mediated activities require both IL-17RB and IL-17RA and provide another example of an IL-17 family ligand that utilizes a heteromeric receptor complex.

Intradermal administration of thymic stromal lymphopoietin induces a T cell- and eosinophil-dependent systemic Th2 inflammatory response.

The epithelial-derived cytokine thymic stromal lymphopoietin (TSLP) is sufficient to induce asthma or atopic dermatitis-like phenotypes when selectively overexpressed in transgenic mice, or when driven by topical application of vitamin D3 or low-calcemic analogues. Although T and B cells have been reported to be dispensable for the TSLP-induced inflammation in these models, little is known about the downstream pathways or additional cell types involved in the inflammatory response driven by TSLP. To characterize the downstream effects of TSLP in vivo, we examined the effects of exogenous administration of TSLP protein to wild-type and genetically deficient mice. TSLP induced a systemic Th2 inflammatory response characterized by increased circulating IgE and IgG1 as well as increased draining lymph node size and cellularity, Th2 cytokine production in draining lymph node cultures, inflammatory cell infiltrates, epithelial hyperplasia, subcuticular fibrosis, and up-regulated Th2 cytokine and chemokine messages in the skin. Responses to TSLP in various genetically deficient mice demonstrated T cells and eosinophils were required, whereas mast cells and TNF-alpha were dispensable. TSLP-induced responses were significantly, but not completely reduced in IL-4- and IL-13-deficient mice. These results shed light on the pathways and cell types involved in TSLP-induced inflammation.

IL-33 amplifies both Th1- and Th2-type responses through its activity on human basophils, allergen-reactive Th2 cells, iNKT and NK cells.

IL-33 is an IL-1 family member recently identified as the ligand for T1/ST2 (ST2), a member of the IL-1 receptor family. ST2 is stably expressed on mast cells and T(h)2 effector T cells and its function has been studied in the context of T(h)2-associated inflammation. Indeed, IL-33 induces T(h)2 cytokines from mast cells and polarized mouse T cells and leads to pulmonary and mucosal T(h)2 inflammation when administered in vivo. To better understand how this pathway modulates inflammatory responses, we examined the activity of IL-33 on a variety of human immune cells. Human blood-derived basophils expressed high levels of ST2 receptor and responded to IL-33 by producing several pro-inflammatory cytokines including IL-1 beta, IL-4, IL-5, IL-6, IL-8, IL-13 and granulocyte macrophage colony-stimulating factor. Next, utilizing a human T(h)2-polarized T cell culture system derived from allergic donor blood cells, we found that IL-33 was able to enhance antigen-dependent and -independent T cell responses, including IL-5, IL-13 and IFN-gamma production. IL-33 activity was also tested on V alpha 24-positive human invariant NKT (iNKT) cells. In the presence of alpha-galactosylceramide antigen presentation, IL-33 dose dependently enhanced iNKT production of several cytokines, including both IL-4 and IFN-gamma. IL-33 also directly induced IFN-gamma production from both iNKT and human NK cells via cooperation with IL-12. Taken together, these results indicate that in addition to its activity on human mast cells, IL-33 is capable of activating human basophils, polarized T cells, iNKT and NK cells. Moreover, the nature of the responses elicited by IL-33 suggests that this axis may amplify both T(h)1- and T(h)2-oriented immune responses.

Novel protein therapeutic joint retention strategy based on collagen-binding Avimers.

Designing drugs to treat diseases associated with articular joints, particularly those targeting chondrocytes, is challenging due to unique local environmental constraints including the avascular nature of cartilage, the absence of a closed joint compartment, and a highly cross-linked extracellular matrix. In an effort to address these challenges, we developed a novel strategy to prolong residence time of intra-articularly administered protein therapeutics. Avimer domains are naturally found in membrane polypeptides and mediate diverse protein-protein interactions. Screening of a phage Avimer domain library led to identification of several low affinity type II collagen-binding Avimers. Following several rounds of mutagenesis and reselection, these initial hits were transformed to high affinity, selective type II collagen-binding Avimers. One such Avimer (M26) persisted in rat knees for at least 1 month following intra-articular administration. Fusion of this Avimer to a candidate therapeutic payload, IL-1Ra, yielded a protein construct which simultaneously bound to type II collagen and to IL-1 receptor. In vitro, IL-1Ra_M26 bound selectively to cartilage explants and remained associated even after extensive washing. Binding appeared to occur preferentially to pericellular regions surrounding chondrocytes. An acute intra-articular IL-1-induced IL-6 challenge rat model was employed to assess in vivo pharmacodynamics. Whereas both IL-1Ra_M26 and native IL-1Ra inhibited IL-6 output when co-administered with the IL-1 challenge, only IL-1Ra_M26 inhibited when administered 1 week prior to IL-1 challenge. Collagen-binding Avimers thus represent a promising strategy for enhancing cartilage residence time of protein therapeutics. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1238-1247, 2018.