Functional Involvement of CD44 Variant 7 in Gut Immune Response

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Abstract
A major problem in inflammatory bowel disease (IBD) is the accumulation of highly activated T-helper cells that are refractory to apoptosis induction. Hence, persistent inflammatory lesions are prevalent and are the basis of chronic disease. In IBD upregulation of costimulatory molecules on lamina propria lymphocytes has been described leading to apoptosis resistance. CD44 is a cell adhesion molecule and a signalling receptor that functions as a costimulatory molecule in T-cell activation. Several variant isoforms of CD44 (CD44v) are expressed by alternative splicing of variant exons encoding extracellular regions. Particularly isoforms containing CD44v7 are expressed on T cells and macrophages in T-helper-1 (Th1)-mediated chronic inflammation and autoimmune diseases. In this review recent data on the functional involvement of CD44v7 isoforms in IBD are discussed. In a mouse model of experimental colitis blockade or deletion of CD44v7 protects mice from severe intestinal inflammation by inducing apoptosis in lamina propria mononuclear cells. Recently, we observed that in lamina propria mononuclear cells from the inflamed but not uninflamed mucosa of patients with Crohn's disease, blockade of CD44v7 isoforms also induces apoptosis. The finding that obstruction of CD44v7 isoforms can antagonize Th1-cytokine-dependent immune pathology identifies CD44v7 as a target in the treatment of inflammatory diseases such as IBD, rheumatoid arthritis, multiple sclerosis and other autoimmune diseases in which CD44v7 isoforms are upregulated.