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Chapter 14 : Regional Immune Response to Microbial Pathogens
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The distribution of organized mucos-aassociated lymphoid tissues (MALT) in mucosal tissues of the body varies among species, but there are certain consistent patterns. The sequence of events involved in processing and presentation of foreign antigens by professional antigen-presenting cells and the responses and interactions of local lymphocytes that lead to the production of effector and memory cells are likely to be similar in the mucosal and systemic branches of the immune system. Alternatively, dendritic cells (DCs) located in the epithelium over organized MALT, such as those that are abundant in the tonsils, could present antigens either in local MALT or after migration to draining lymph nodes. In addition, the class I-related molecule CD1d is expressed at the basolateral surfaces of intestinal epithelial cells and appears to function as an antigen presenting molecule by interacting with specialized populations of T cells. The possible role of antigen uptake by enterocytes in induction of immune responses or immune tolerance is discussed. The mucosal addressin MadCam-1 (mucosal addressin cell adhesion molecule 1) is preferentially expressed in human and mouse intestinal flat postcapillary venules of the lamina propria and high endothelial venules of organized MALT but not in other mucosal tissues. When microbial pathogens adhere to or invade the epithelial cells that line mucosal surfaces, the cells release proinflammatory cytokines and chemokines and upregulate chemokine receptors and adhesion molecules.