Frank Maas


The vermiform appendix Is purported to be the classic example of a vestigial organ, yet for nearly a century it has been known to be a specialized organ highly infiltrated with lymphoid tissue. This lymphoid tissue may help protect against local gut infections. As the vertebrate taxonomic scale increases, the lymphoid tissue of the large bowel tends to be concentrated In a specific region of the gut: the cecal apex or vermiform appendix. The rabbit appendix has the greatest relative lymphoid development. Neonatal appendectomy in rabbits results in decreased total lymphocyte counts and lower antibody response to immune challenges relative to sham-operated controls. Appendectomy in young adult rabbits subject to whole body irradiation also depresses immunocompetence. The ultrastructure of the rabbit and human appendix mirrors that of Peyer's patches and the avian bursa of Fabricius. The appendix shares secondary functions of the avian bursa: it transports antigens from the intestinal lumen to the lamina propria; these antigens stimulate B cell proliferation, dissemination throughout the gut-associated lymphoid tissues, and differentiation into antibody secreting cells. In vitro studies indicate the human appendix contains immunocompetent B cells, T cells and natural killer cells. It is also a major site of IgA induction. Several epidemiologic studies suggest a correlation between appendectomy and cancer risk but these findings are inconclusive. Incidental appendectomy is often practiced by physicians despite the growing evidence that the appendix may be an Important component of the immune system.


Mucosal immunology, gut-associated lymphoid tissues. immunocompetence, appendix (human and rabbit), appendectomy, neoplasm, vestigial organ


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