IL-4 Signaling Pathway Regulation of Sjogren's Syndrome

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DESCRIPTION: Sjogren's syndrome is a human autoimmune disease characterized by exocrine dysfunction resulting from the action of1 a chronic autoimmune attack against the lacrimal and salivary glands. It is one of the leading causes of salivary gland inflammation and dysfunction, leading to severe dryness of the ocular and oral surfaces. Diagnosis of Sjogren's syndrome includes detection of leukocytic infiltrates in the minor salivary glands, the presence of rheumatoid factor, hypergammaglobulinemia, specific anti-nuclear autoantibodies, loss of stimulated fluid secretion, and complaints of dry eyes and/or dry mouth. Over the past several years, the NOD mouse has been shown to exhibit numerous disease manifestations that parallel Sjogren's syndrome, including loss of stimulated fluid secretion concomitant with the appearance of leukocyte infiltrates in the lacrimal and salivary glands. Studies of autoimmune exocrinopathy in NOD mice have revealed that the disease can be separated into two phases: Phase 1 is characterized by pathophysiological and biochemical changes in the exude glands whose occurrence are independent of the autoimmune attack. Phase 2 is characterized by the appearance of leukocytic infiltrates in the exocrine glands, proinflammatory responses, autoantibodies to multiple acinar cell components, loss of acinar cell mass, and decline in exocrine function. The use of specific gene knockout mice congenic with the parental NOD mouse strain indicated that loss of exocrine function was dependent, first, on the presence of B cells and, second, expression of the intedeukin-4 (IL-4) cytokine. Subsequent studies suggested that IL-4 exerted its activity by regulating antibody isotypic class switching in B ceils. Nevertheless, IL-4 can activate two distinct signaling pathways in B ceils: the STAT-6 and the IRS pathways. The STAT-6 signaling pathway is involved in antibody class switching, while the IRS pathway is involved in B cell maturation and clonal deletion. Thus, the purpose of the current R21 grant application is to initiate studies examining the mechanism(s) by which IL-4 elicits its effector function in the development of exocrine gland dysfunction and decreased fluid secretion. Specifically, we plan to (t) document the autoimmune phenotype of a newly constructed NOD.B10.H-2b.B/c-STAT6 knockout mouse line and compare this phenotype to NOD.B10.H-2b, NOD.B10.H-2b.lgp KO and NOD.B10.H-2b.IL4 KO mice, and (2) identify if the IL-4 dependent development of exocrine gland dysfunction is due to activation of the STAT-6, IRS or both signal transduction pathway(s). Results from these studies will provide insight into the role of the cytokine, IL-4, and its effector mechanism in regulating development of the pathogenesis of Sjgren's syndrome. Identification of this effector mechanism could be important to the long-term goal of developing targeted preventive or early intervention strategies.