In vivo regulation of the allergic response by the IL-4 receptor alpha chain immunoreceptor tyrosine-based inhibitory motif.

BACKGROUND: Signaling by IL-4 and IL-13 through the IL-4 receptor alpha chain (IL-4Ralpha) plays a critical role in the pathology of allergic diseases. The IL-4Ralpha is endowed with an immunoreceptor tyrosine-based inhibitory motif (ITIM) centered on tyrosine 709 (Y709) in the cytoplasmic domain that binds a number of regulatory phosphatases. The function of the ITIM in the in vivo regulation of IL-4 receptor signaling remains unknown. OBJECTIVE: We sought to determine the in vivo function of the IL-4Ralpha ITIM by using mice in which the ITIM was inactivated by mutagenesis of the tyrosine Y709 residue into phenylalanine (F709). METHODS: F709 ITIM mutant mice were derived by means of knock-in mutagenesis. Activation of intracellular signaling cascades by IL-4 and IL-13 was assessed by means of intracellular staining of phosphorylated signaling intermediates and gene expression analysis. In vivo responses to allergic sensitization were assessed by using models of allergic airway inflammation. RESULTS: The F709 mutation increased signal transducer and activator of transcription 6 phosphorylation by IL-4 and, disproportionately, by IL-13. This was associated with exaggerated T(H)2 polarization, enhanced alternative macrophage activation by IL-13, augmented basal and antigen-induced IgE responses, and intensified allergen-induced eosinophilic airway inflammation and hyperreactivity. CONCLUSIONS: These results point to a physiologic negative regulatory role for the Y709 ITIM in signaling through IL-4Ralpha, especially by IL-13.

Pathogenicity of a disease-associated human IL-4 receptor allele in experimental asthma.

Polymorphisms in the interleukin-4 receptor alpha chain (IL-4R alpha) have been linked to asthma incidence and severity, but a causal relationship has remained uncertain. In particular, a glutamine to arginine substitution at position 576 (Q576R) of IL-4R alpha has been associated with severe asthma, especially in African Americans. We show that mice carrying the Q576R polymorphism exhibited intense allergen-induced airway inflammation and remodeling. The Q576R polymorphism did not affect proximal signal transducer and activator of transcription (STAT) 6 activation, but synergized with STAT6 in a gene target- and tissue-specific manner to mediate heightened expression of a subset of IL-4- and IL-13-responsive genes involved in allergic inflammation. Our findings indicate that the Q576R polymorphism directly promotes asthma in carrier populations by selectively augmenting IL-4R alpha-dependent signaling.

Defects along the T(H)17 differentiation pathway underlie genetically distinct forms of the hyper IgE syndrome.

BACKGROUND: The hyper IgE syndrome (HIES) is characterized by abscesses, eczema, recurrent infections, skeletal and connective tissue abnormalities, elevated serum IgE, and diminished inflammatory responses. It exists as autosomal-dominant and autosomal-recessive forms that manifest common and distinguishing clinical features. A majority of those with autosomal-dominant HIES have heterozygous mutations in signal transducer and activator of transcription (STAT)-3 and impaired T(H)17 differentiation. OBJECTIVE: To elucidate mechanisms underlying different forms of HIES. METHODS: A cohort of 25 Turkish children diagnosed with HIES were examined for STAT3 mutations by DNA sequencing. Activation of STAT3 by IL-6 and IL-21 and STAT1 by IFN-alpha was assessed by intracellular staining with anti-phospho (p)STAT3 and -pSTAT1 antibodies. T(H)17 and T(H)1 cell differentiation was assessed by measuring the production of IL-17 and IFN-gamma, respectively. RESULTS: Six subjects had STAT3 mutations affecting the DNA binding, Src homology 2, and transactivation domains, including 3 novel ones. Mutation-positive but not mutation-negative subjects with HIES exhibited reduced phosphorylation of STAT3 in response to cytokine stimulation, whereas pSTAT1 activation was unaffected. Both patient groups exhibited impaired T(H)17 responses, but whereas STAT3 mutations abrogated early steps in T(H)17 differentiation, the defects in patients with HIES with normal STAT3 affected more distal steps. CONCLUSION: In this cohort of Turkish children with HIES, a majority had normal STAT3, implicating other targets in disease pathogenesis. Impaired T(H)17 responses were evident irrespective of the STAT3 mutation status, indicating that different genetic forms of HIES share a common functional outcome.

Humanized anti-interleukin-2 (IL-2) receptor alpha therapy: long-term results in uveitis patients and preliminary safety and activity data for establishing parameters for subcutaneous administration.

Therapy for severe uveitis is frequently long-term immunosuppression using systemic corticosteroids and cytotoxic agents, but side effects make long-term therapy difficult. A long-term (>4 year) Phase I/II single armed interventional study using intravenous anti-IL-2 receptor alpha treatments (daclizumab) and a short-term Phase II study evaluating the use of a subcutaneous daclizumab formulation were conducted. Patients were tapered off their systemic immunosuppressive therapy and received daclizumab infusions or subcutaneous injections at intervals varying from 2 to 6 weeks. In the long-term study, seven of ten enrolled patients were tapered from their original immunosuppressive medications and maintained exclusively on repeated daclizumab infusions for control of their uveitis for over 4 years. No patient was permanently removed from therapy for an adverse event ascribed to the medication. The use of 6-week infusion intervals led to recurrence of uveitis, while 2- to 4-week intervals did not. Only one patient developed measurable anti-daclizumab antibodies but this disappeared when subcutaneous therapy was begun. In the short-term study, four of the five patients receiving the subcutaneous formulation met the study endpoints for success within the first 12 weeks. All five were successful by 26 weeks. These studies provide preliminary evidence that regularly administered long-term daclizumab therapy can be given in lieu of standard immunosuppression for years to treat severe uveitis and that subcutaneously administered daclizumab appeared to be a clinically viable treatment strategy. These studies suggest that anti-IL-2 receptor blockade could be useful in the treatment of Th1-mediated autoimmune conditions.

Mycophenolate mofetil for the treatment of scleritis.

PURPOSE: To evaluate the usefulness of mycophenolate mofetil (MMF) (CellCept, Roche, Nutley, NJ), an antimetabolite immunosuppressant with a selective antiproliferative effect on T and B lymphocytes, for the treatment of scleritis. DESIGN: Retrospective, noncomparative case series. PARTICIPANTS: Eight patients with scleritis treated with MMF in a tertiary referral center. METHODS: Review of the clinical records of patients evaluated at the National Eye Institute and prescribed MMF for the treatment of scleritis. MAIN OUTCOME MEASURES: Control of scleral inflammation, the ability to taper prednisone or other immunosuppressive medications, and adverse events were recorded for each patient. Mycophenolate mofetil was determined to be an effective steroid-sparing agent if the daily prednisone dosage could be reduced by 50% or more and was determined to be an effective adjunctive immunosuppressive agent if the scleral inflammation was controlled in patients with active scleritis. RESULTS: Four patients with diffuse anterior scleritis, two with necrotizing scleritis with inflammation, one with nodular anterior scleritis, and one with nodular anterior and posterior scleritis, were identified. Mycophenolate mofetil administration was initiated as a steroid-sparing agent in 4 patients with controlled scleritis and as an additional immunosuppressive agent in 4 patients with active scleritis receiving concomitant treatment with prednisone and cyclosporine or methotrexate. In 3 of the 4 patients started on MMF as a steroid-sparing agent, the scleritis remained controlled while the prednisone dosage was tapered by more than 50%. One of the patients started on MMF as a steroid-sparing agent had recurrent scleritis, and each of the patients with active scleritis continued to have persistent scleral inflammation requiring additional immunosuppressive therapy. Adverse effects recorded in 4 of the 8 patients included a rash, gastrointestinal symptoms, paresthesias, and laboratory evidence of hepatotoxicity and renal toxicity. CONCLUSIONS: Although MMF maybe be useful as a steroid-sparing agent, it was not effective as an adjunctive immunosuppressive agent in patients with active scleritis in our small, tertiary referral series. The adverse effects encountered with the use of MMF in this study cannot be attributed conclusively to MMF and are more likely complications of the multiagent systemic immunosuppressive therapy required for the treatment of recalcitrant scleritis.