A crypto-lymphatic unit at the uvula of the monkey Macaca fascicularis. A light- and electron-microscopic study.

A crypto-lymphatic unit was observed at the left lateral aspect of the uvula of a mature female monkey, Macaca fascicularis. A light- and transmission electron-microscopic investigation revealed that the lumen of the crypt was filled with bacteria, desquamated epithelial cells, lymphocytes and neutrophils. The non-keratinized stratified squamous epithelium of the crypt was fragmented and showed heavy mononuclear cell infiltration and surface discontinuities, exposing lymphoid cells to foreign material. The lymphatic parenchyma consisted of organized lymphatic tissue including germinal centres. The resident cell population included lymphocytes of varying size, blastforming B- and T-lymphocytes and two types of reticular cells resembling the fibroblastic reticulum cell and the follicular dendritic cell, respectively. Occasionally granulocytes were encountered. At its base and laterally the crypto-lymphatic unit was ensheathed by a thin connective tissue capsule. Three other monkeys of the same species failed to reveal similar structures at the same site.