Morphological Studies on the Postnatal Development of the Gut-associated Lymphoid Tissues of the Rabbit Cecum

Abstract

The macroscopic, morphometric, light and scanning electron microscopic structure of gut-associated lymphoid tissue (GALT) of cecum were studied in the rabbits aged from birth to 16 weeks. The GALT were formed of lymph follicles covered by low columnar epithelium containing intraepithelial lymphocytes and leukocytes. They were concentrated at the ileocecal entrance (ileocecal patch) and in the blind end of the cecum vermiform appendix. In the ileocecal patch, GALT were in direct contact with the lumen, while those of the appendix were covered by the interval intestinal villi in young rabbits and mucosal folds in the adult rabbits. The lymphoid follicles of the ileocecal patch were composed of dome region and germinal center and were separated by narrow inter-follicular areas. Whereas, the lymphoid follicles of the appendix were composed dome region and germinal center in the newly born rabbits and up to the 2nd week of age, the follicles became composed of four different sites: dome region, germinal center, coronal area, and a wide interfollicular area between neighboring follicles. Morphometrically; the dimensions of the lymphoid follicles of the cecal GALT increased in size with the advancement of the age. By SEM the lymphoid structures covered with special epithelium consisted of two types of cell absorptive enterocytes and M cells. The M cells in the cecal patch were microvilliated and present on the tips and sides of the dome lymphoid regions while in the appendix were non-microvilliated and present only on the sides of the dome regions.