DISTINCTIVE ADHESION PATHWAYS ARE INVOLVED IN EPITHELIOTROPIC PROCESSES AT DIFFERENT SITES

Intraepithelial migration of lymphoid cells (epitheliotropism) is a biological process that can be observed under various physiological and pathological conditions. Recently, epitheliotropism was proposed to be a multi‐step process, involving interactions of lymphoid cells with both epithelial basement membrane (EBM) and epithelial cells. In the present study we analysed by immunohistochemistry the adhesion mechanisms that are potentially involved in epitheliotropism of lymphoid cells in various disorders, such as tonsillar hyperplasia, coeliac disease, malignant lymphomas of mucosa‐associated lymphoid tissue (MALTomas), and mycosis fungoides (MF). The combinations of adhesion molecules expressed on the participating lymphoid and epithelial cells varied among these disorders. These findings suggest the adhesion pathways utilized in epitheliotropism may be associated with the nature of the lymphoid cell (reactive or neoplastic/B or T) and/or the site of the epithelium involved. In some cases the specificity of the process was determined by the adhesion mechanism involved in the lymphocyte–EBM interaction, as in the case of α3β1 integrin/laminin‐5 in MF, and in others by the adhesion mechanisms involved in the interaction between lymphoid and epithelial cells, such as α4 integrin/VCAM‐1 in tonsillar hyperplasia and αEβ7/E‐cadherin in coeliac disease.