IMMUNOLOGY AND MOLECULAR BIOLOGY Esophageal Tonsil: A Novel Gut-Associated Lymphoid Organ

The esophageal tonsil of the chicken is a novel, significant element of the gut-associated lymphoid tissue (GALT). Its stable location and histological organi- zation fulfills the meaning of the term "tonsil." The six- to-eight-isolated tonsillar units are located at the border of the esophagus and the proventriculus. The number of tonsillar units is identical with that of the esophageal folds. Each tonsillar unit consists of a crypt lined by lymphoepithelium and surrounded by dense lymphoid tissue, which is organized into T- and B-dependent re-