FIGURE 2

Illustration of three mucosal immune-cell compartments. (a,b) Three-color immunofluorescence staining of B cells (CD20, green), T cells (CD3, red), and epithelium (cytokeratin, blue) in cryosection of human Peyer's patch. (b) Details from the M-cell areas framed on the left in the follicle-associated epithelium (a) covering a B-cell follicle. (c) Two-color immunofluorescence staining for IgA (green) and IgG (red) in a section from normal human large bowel mucosa. Crypt epithelium shows selective transport of IgA, and only a few scattered IgG-producing cells are seen in the lamina propria together with numerous IgA plasma cells. (d) Three-color immunofluorescence staining for CD4⁺ (red) and CD8⁺ (green) T cells in normal human duodenal mucosa. The epithelium of the villi is blue (cytokeratin). Note that most of the elements with weak CD4 expression seen in the background are either macrophages or dendritic cells. The immunofluorescence pictures are original images from the Brandtzaeg laboratory, reproduced from Brandtzaeg and Pabst¹ with permission from Elsevier.