Inflammation may be an acute or chronic, localized or systemic immune and/or vascular response to trauma or infection by microbes, such as bacterial or viruses. Inflammatory reactions typically destroy, dilute, or confine the injurious agent and the injured tissue in the subject. Inflammation is characterized, particularly in the acute form, by the classic signs of pain, heat, redness, swelling, and possibly loss of function. At a histological level, inflammation involves a complex series of events, including dilation of arterioles, capillaries, and venules, and an increased permeability and blood flow, exudation of fluids, including plasma proteins, and leukocyte migration into the area of inflammation, particularly with a localized reaction.
Therapeutic treatments for inflammation include a wide array of pharmaceutical drugs administered intravenously, subcutaneously, topically, or orally, depending on the particular inflammatory condition and outcome sought. However, most of the anti-inflammatory treatments available today have considerable drawbacks, including severe reactions at injection site, increased susceptibility to infection, rash, or other side effects. Thus, there is a need for better anti-inflammatory therapeutics and treatment methods.
Thymic Stromal Lymphopoietin (TSLP).
Thymic stromal lymphopoietin (TSLP) is an IL-7-like cytokine that triggers dendritic cell-mediated Th2-type inflammatory responses and is considered as a master switch for allergic inflammation. TSLP is an integral growth factor to both B and T cell development and maturation. Particularly, murine TSLP supports B lymphopoieses and is required for B cell proliferation. Murine TSLP plays a crucial role in controlling the rearrangement of the T cell receptor-gamma (TCR.gamma.) locus and has a substantial stimulatory effect on thymocytes and mature T cells. See, for example, Friend et al., Exp. Hematol., 22:321-328, 1994; Ray et al., Eur. J. Immunol., 26:10-16, 1996; Candeias et al., Immunology Letters, 57:9-14, 1997.
TSLP possesses cytokine activity similar to IL-7. For instance, TSLP can replace IL-7 in stimulating B cell proliferation responses (Friend et al., supra). Although TSLP and IL-7 mediate similar effects on target cells, they appear to have distinct signaling pathways and likely vary in their biologic response. For Example, although TSLP modulates the activity of STAT5, it fails to activate any Janus family tyrosine kinase members (Levin et. al., J. Immunol., 162:677-683, 1999).
TSLP Effects on Dendritic Cells and TNF Production.
After human TSLP and the human TSLP receptor were cloned in 2001, it was discovered that human TSLP potently activated immature CD11c+ myeloid dendritic cells (mDCs) (see, e.g., Reche et al., J. Immunol., 167:336-343, 2001 and Soumelis et al., Nat. Immunol., 3:673-680, 2002). Th2 cells are generally defined in immunology textbooks and literature as CD4+ T cells that produce IL-4, IL-5, IL-13, and IL-10. And Th1 cells such as CD4+ T cells produce IFN-γ and sometimes TNF. When TSLP-DCs are used to stimulate naive allogeneic CD4+ T cells in vitro, a unique type of Th2 cell is induced which produces the classical Th2 cytokines IL-4, IL-5, and IL-13, and large amounts of TNF, but little or no IL-10 or interferon-γ (Reche et al., Supra) (see also, e.g., Soumelis et al., Nat. Immunol., 3:673-680, 2002). TNF is not typically considered a Th2 cytokine. However, TNF is prominent in asthmatic airways and genotypes that correlate with increased TNF secretion are associated with an increased asthma risk. See Shah et al., Clin. Exp. Allergy., 25:1038-1044, 1995 and Moffatt, M. F. and Cookson, W. O., Hum. Mol. Genet., 6:551-554, 1997.
TSLP induces human mDCs to express the TNF superfamily protein OX40L at both the mRNA and protein level (Ito et al., J. Exp. Med., 202:1213-1223). The expression of OX40L by TSLP-DCs is important for the elaboration of inflammatory Th2 cells. Thus, TSLP-activated DCs create a Th2-permissive microenvironment by up-regulating OX40L without inducing the production of Th1-polarizing cytokines. Id.
TSLP Expression, Allergen-Specific Responses and Asthma.
in Early studies have shown that TSLP mRNA was highly expressed by human primary skin keratinocytes, bronchial epithelial cells, smooth muscle cells, and lung fibroblasts (Soumelis et al., Nat. Immunol., 3:673-680, 2002). Because TSLP is expressed mainly in keratinocytes of the apical layers of the epidermis, this suggests that TSLP production is a feature of fully differentiated keratinocytes. TSLP expression in patients with atopic dermatitis was associated with Langerhans cell migration and activation in situ which suggests that TSLP may contribute directly to the activation of these cells which could subsequently migrate into the draining lymph nodes and prime allergen-specific responses. Id. In a more recent study, it was shown by in situ hybridization that TSLP expression was increased in asthmatic airways and correlated with both the expression of Th2-attracting chomokines and with disease severity which provided a link between TSLP and asthma (Ying et al., J. Immunol., 174:8183-8190, 2005).
TSLP Receptor (TSLPR) and Allergy, Asthma.
The TSLP receptor (TSLPR) is approximately 50 kDa protein and has significant similarity to the common γ-chain. TSLPR is a novel type 1 cytokine receptor, which, combined with IL-7Rα (CD127), constitutes a TSLP receptor complex as described, for example, in Pandey et al., Nat. Immunol., 1:59-64, 2000. TSLPR has a tyrosine residue near its carboxyl terminus, which can associate with phosphorylated STAT5 and mediate multiple biological functions when engaged with TSLP (Isaksen et al., J. Immunol., 168:3288-3294, 2002).
Human TSLPR is expressed by monocytes and CD11c+ dendritic cells, and TSLP binding induces the expression of the TH2 cell-attracting chemokines CCL17 and CCL22. Furthermore, as stated above, the TSLPR-induced activation of dendritic cells indirectly results in the increased secretion of TH2 cytokines IL-4, -5 and -13, which may be necessary for the regulation of CD4+ T cell homeostasis. In mice, deficiency of TSLPR has no effect on lymphocyte numbers. However, a deficiency of TSLPR and common γ-chain results in fewer lymphocytes as compared to mice deficient in the common γ-chain alone. See Reche et al., J. Immunol., 167:336-343, 2001 and Soumelis et al., Nat. Immunol., 3:673-680, 2002.
Studies have found that TSLP and the TSLPR play a critical role in the initiation of allergic diseases in mice. In one study, it was demonstrated that mice engineered to overexpress TSLP in the skin developed atopic dermatitis which is characterized by eczematous skin lesions containing inflammatory infiltrates, a dramatic increase in circulating Th2 cells and elevated serum IgE (Yoo et al., J. Exp. Med., 202:541-549, 2005). The study suggested that TSLP may directly activate DCs in mice. In another study, conducted by Li et al., the group confirmed that transgenic mice overexpressing TSLP in the skin developed atopic dermatitis which solidifies the link between TSLP and the development of atopic dermatitis.
Another set of studies demonstrated that TSLP is required for the initiation of allergic airway inflammation in mice in vivo. In one study, Zhou et al. demonstrated that lunch specific expression of a TSLP transgene induced allergic airway inflammation (asthma) which is characterized by massive infiltration of leukocytes (including Th2 cells), goblet cell hyperplasia, and subepithelial fibrosis, and increased serum IgE levels (Zhou et al., Nat. Immunol., 6:1047-1053, 2005). However, in contrast, mice lacking the TSLPR failed to develop asthma in response to inhaled antigens (Zhou et al., supra and Al-Shami et al., J. Exp. Med., 202:829-839, 2005). Thus, these studies together demonstrate that TSLP is required for the initiation of allergic airway inflammation in mice.
Further, in a study conducted by Yong-Jun et al., it was demonstrated that epithelial cell-derived TSLP triggers DC-mediated inflammatory Th2 responses in humans which suggest that TSLP represents a master switch of allergic inflammation at the epithelial cell-DC interface (Yong-Jun et al., J. Exp. Med., 203:269-273, 2006).
In a recent study, it was shown that modulation of DCs function by inhibiting TSLPR lessened the severity in mice (Liyun Shi et al., Clin. Immunol., 129:202-210, 2008). In another set of studies, it was demonstrated that TSLPR was not only expressed in DCs, but also on macrophages, mast cells, and CD4+ T cells (Rochman et al., J. Immunol., 178:6720-6724, 2007 and Omori M. and Ziegler S., J. Immunol., 178:1396-1404, 2007). In order to rule out the direct effects of TSLPR neutralization on CD4+ T cells or other effector cells in allergic inflammation, Liyun Shi et al. performed experiments wherein OVA-loaded DCs were in vitro treated with anti-TSLPR before adoptive transfer to the airways of naive mice. It has previously been found that OVA-DCs triggered strong eosinophilic airway inflammation and accompanied with massive production of Th2 cytokines such as IL-4 and IL-5 (Sung et al., J. Immunol., 166:1261-1271 and Lambrecht et al., J. Clin. Invest., 106:551-559, 2000). However, pretreating OVA-DCs with anti-TSLPR resulted in a significant reduction of eosinophils and lymphocyte infiltration as well as IL-4 and IL-5 levels, further illuminating the role that TSLPR plays in DC-primed allergic disease. This result also supports that blocking of TSLPR on DCs will aid in controlling airway inflammation (Liyun Shi et al., supra).
There has been a growing body of experiments implicating the role of TSLP/TSLPR in various physiological and pathological processes. Physiological roles of TSLP include modulating the immune system, particularly in stimulating B and T cell proliferation, development, and maturation. TSLP plays a vital role in the pathobiology of allergic asthma and local antibody mediated blockade of TSLP receptor function to alleviate allergic diseases. Thus, interplay between TSLP and TSLP receptor is believed to be important in many physiological disease processes such as: allergic inflammation, skin lesions of patients with atopic dermatitis or atopic eczema, and asthma.