Phenotypic and functional characterisation of follicle-associated epithelium of rectal lymphoid tissue

Lymphoid follicles cluster in the terminal rectum of various animal species and of man and hence this site may be important in the development of immune responses to pathogens. For the induction of immune responses at mucosal sites, interplay is required between various cell types performing functions ranging from antigen-sampling cells via antigen-presenting cells to antigen-specific lymphocytes. Therefore, we have characterised the cell populations and relevant functioning of follicle-associated epithelium (FAE) and associated follicles in the terminal portion of rectum in cattle as a representative mammal. Immunohistochemical studies of this region identified immune cell subsets (CD4+, CD8+, WC1+γδ, CD2+, CD21+ and CD40+ cells) characteristic of an immune-inductive site. Examination of FAE identified a subset of cells with structural and functional features of antigen-sampling M-cells. Cells of the FAE and adjacent follicle-associated crypts expressed vimentin and a subset of these cells internalised microparticles, a further attribute of M-cells. The FAE cells were phenotypically heterogeneous and therefore the function and phenotype of these cell subsets requires further characterisation, particularly with respect to their potentially important role in the interaction of hosts with pathogens and the development of immune responses

Interaction of Shiga toxin from Escherichia coli with human intestinal epithelial cell lines and explants: Stx2 induces epithelial damage in organ culture

Shiga toxins (Stx) produced by Escherichia coli are associated with systemic complications such as haemolytic-uraemic syndrome. The mechanism of Stx translocation across the epithelial barrier is unknown as human intestinal epithelium lacks receptor Gb3. In this study, we have examined the interaction of purified Stx1 and 2 with Caco-2 (Gb3(+)) and T84 (Gb3(-)) cell lines, and determined the effects of Stx on human intestine using in vitro organ culture (IVOC). Stx exposure caused inhibition of protein synthesis and apoptosis in Caco-2 but not in T84 cells. However, both Stx1 and 2 were transported to the endoplasmic reticulum, and the Stx1 A-subunit was cleaved in a furin-dependent manner in both cell lines. Thus, a Gb3-independent retrograde transport route exists in T84 cells for Stx that does not induce cell damage. IVOC demonstrated increased epithelial cell extrusion in response to exposure to Stx2, but not Stx1, in both small intestine and colon. Pretreatment of Stx2 with Stx2-specific antibody abrogated this effect. Overlaying frozen sections with Stx showed lamina propria, but not epithelial, cell binding that paralleled Gb3 localization, and included endothelium and pericryptal myofibroblasts. This indicates that human intestinal epithelium may evince Stx2-induced damage in the absence of Gb3 receptors, by an as yet unrecognized mechanism