Cynthia Mueller

Attenuation of Immunological Symptoms of Allergic Asthma in Mice Lacking the Tyrosine Kinase ITK

Allergic asthma patients manifest airway inflammation and some show increases in eosinophils, TH2 cells, and cytokines, increased mucous production in the lung, and elevated serum IgE. This TH2-type response suggests a prominent role for TH2 cells and their cytokines in the pathology of this disease. The Tec family nonreceptor tyrosine kinase inducible T cell kinase (ITK) has been shown to play a role in the differentiation and/or function of TH2-type cells, suggesting that ITK may represent a good target for the control of asthma. Using a murine model of allergic asthma, we show here that ITK is involved in the development of immunological symptoms seen in this model. We show that mice lacking ITK have drastically reduced lung inflammation, eosinophil infiltration, and mucous production following induction of allergic asthma. Notably, T cell influx into the lung was reduced in mice lacking ITK. T cells from ITK−/− mice also exhibited reduced proliferation and cytokine secretion, in particular IL-5 and IL-13, in response to challenge with the allergen OVA, despite elevated levels of total IgE and increased OVA-specific IgE responses. Our results suggest that the tyrosine kinase ITK preferentially regulates the secretion of the TH2 cytokines IL-5 and IL-13 and may be an attractive target for antiasthmatic drugs.

Opposing roles of serine/threonine kinases MEKK1 and LOK in regulating the CD28 responsive element in T-cells

T-cell activation requires signals from both the T-cell receptor (TcR) and other co-stimulatory molecules such as CD28. TcR- and CD28-mediated signals are integrated during T-cell activation resulting in the expression of cytokine genes such as interleukin-2 (IL-2). An enhancer element (CD28RE) of the IL-2 gene specifically responsive to CD28 signals has been previously identified and characterized. This response element and an adjacent Activated Protein-1 (nuclear factor-interleukin-2B) site together (RE/AP1) were shown to complex with c-rel, AP-1 and other factors. However, details of the signal transduction pathways leading from CD28 to the composite response element remain poorly understood. We present data showing that overexpression of the serine threonine kinase, mitogen-activated protein kinase/extracellular-signal-regulated kinase kinase kinase-1 (MEKK1), but not nuclear factor-kappa B inducing kinase, or MAP kinase/ERK kinase-1 (MEK1), can significantly increase the level of CD28RE/AP1-driven luciferase (Luc) reporter gene expression in Jurkat E6-1 cells. A MEKK1 dominant negative mutant blocked such activation induced by stimulation with Raji B cells and the superantigen staphylococcus enterotoxin E (SEE), as well as via CD3/CD28. Mutations in either site of the RE/AP1 element abolished MEKK1-induced Luc expression. Calcineurin inhibitors, CsA and FK520, or inhibitors of p38 kinase (SB 203580), or MEK1 (PD 098059), did not affect MEKK1-induced reporter activation. These results directly implicate MEKK1 in the CD28 signalling pathway that activates the CD28 response element. Co-expression of the lymphocyte-oriented kinase (LOK) kinase attenuated Raji/SEE-induced IL-2 production in Jurkat cells, as well as MEKK1 and Raji/SEE-induced reporter gene activation. These data suggest that MEKK1 and LOK may have opposing roles in regulating the CD28RE/AP1 element.

Differential sensitivity to Itk kinase signals for T helper 2 cytokine production and chemokine-mediated migration.

Allergic asthma is dependent on chemokine-mediated Th2 cell migration and Th2 cytokine secretion into the lungs. The inducible T cell tyrosine kinase Itk regulates the production of Th2 cytokines as well as migration in response to chemokine gradients. Mice lacking Itk are resistant to developing allergic asthma. However, the role of kinase activity of Itk in the development of this disease is unclear. In addition, whether distinct Itk-derived signals lead to T cell migration and secretion of Th2 cytokines is also unknown. Using transgenic mice specifically lacking Itk kinase activity, we show that active kinase signaling is required for control of Th2 responses and development of allergic asthma. Moreover, dominant suppression of kinase Itk activity led to normal Th2 responses, but significantly reduced chemokine-mediated migration, resulting in prevention of allergic asthma. These observations indicate that signals required for Th2 responses and migration are differentially sensitive to Itk activity. Manipulation of Itk’s activity can thus provide a new strategy to treat allergic asthma by differentially affecting migration of T cells into the lungs, leaving Th2 responses intact.

The Tec family of tyrosine kinases in T cells, amplifiers of T cell receptor signals.

ITK and Rlk/Txk are the predominant Tec family of tyrosine kinases expressed in T cells, and are involved in T cell antigen receptor mediated activation of T cells. These kinases require prior activation of Lck, Zap-70 and PI3-kinase for efficient activation. They share major substrates with both Lck and Zap-70, however the pathways they regulate are unclear. Recent evidence suggests that these kinases may not activate unique pathways, but instead serve as amplifiers for the upstream kinases Lck and Zap-70. This review will discuss the evidence for this view.