The densities of IgG-, IgA-, IgM- and IgD-producing immunocytes were determined by paired immunofluorescence staining and morphometric analysis in the lamina propria of normal appendix specimens. Normal colon specimens were used as reference material, mostly paired from individual subjects. The density (median of cells/mm2 lamina propria area) of IgA immunocytes tended to be slightly higher in the appendix than in the colon (1259 vs 962) and the same held true for IgM cells (71 vs 55). Conversely, the overall density of IgG immunocytes was much higher in the appendix than in the colon (95 vs 38). A striking feature was the fact that almost 50% of all immunocytes were of the IgG isotype adjacent to lymphoid follicles. It seemed justified to conclude, therefore, that the abundance of such follicles explains the overall enrichment of IgG-producing cells in normal appendix mucosa. These immunocytes most likely represent follicle derived B cells that have reached terminal maturation locally, whereas precursors generated from less mature memory clones probably emigrate and home ubiquitously to distant sites of the gut lamina propria where they develop into IgA-producing immunocytes.
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