Intestinal Mucosal Lymphocytes: A New Approach to the Pathogenesis of Inflammatory Bowel Disease

Abstract

Among the several theories proposed to explain the pathogenesis of inflammatory bowel disease (IBD), one of the most prominent has been that proposing that both Crohn’s disease (CD) and ulcerative colitis (UC) are caused by immunological abnormalities. Until less than a decade ago, most experimental studies aimed at the investigation of the immune status of patients with IBD had been restricted to the assessment of in vitro functional characteristics of the mononuclear cells present in the peripheral circulation. This was due to technical limitations of the study of the lymphoid tissue of human intestine, where the actual activity of the disease is centered, and where fundamental immunological events are likely to take place. Advancement in immunological methodology, such as development of antigen-specific monoclonal antibodies, techniques to reliably and specifically stain lymphoid cell subsets in tissue section, and most of all, the ability to retrieve large numbers of viable and functional mononuclear cells directly from the mucosa have drastically changed the approach to the study of immune function in IBD. This field has thus witnessed a significant change in the last few years, as most investigators switched the focus of their research from peripheral blood to the intestinal mucosa. This chapter will review and update the knowledge acquired from in loco and in vitro studies of human intestinal mucosal lymphoid cells, with special emphasis on the potential relevance of these findings to both CD and UC.