Bacillary characteristics in Whipple's disease: an electron microscopic study.

Extensive electron microscopic observations of 19 intestinal biopsies obtained from 13 patients with untreated Whipple's disease are reported. The outstanding feature is the profuse presence of bacilli free within the lamina propria of the intestinal mucosa and the presence of numerous macrophages containing ingested bacilli. Intestinal epithelial cell invasion by bacilli is identified in 11 patients, and evidence of bacillary invasion is identified within the lymphatic endothelium of 4 patients, within capillary endothelium of 3 patients, within polymorphonuclear leukocytes of 5 patients, and within plasma cells of 2 patients. Reported for the first time is the presence of bacilli within intrinsic smooth muscle of the lamina propria of 2 patients, within intraepithelial lymphocytes of 1 patient, and in mast cells of 1 patient. These observations suggest that the Whipple bacillus is an intracellular pathogen. Intracellular pathogens, unlike pyogenic bacteria, may survive within macrophages. The morphologic appearance of the Whipple bacillus is reviewed. Emphasis is placed upon the unique nature of an outer "membrane" external to the cell wall of Whipple bacilli, a feature that is one of the identifying characteristics of the Whipple bacillus and that may explain the inability to culture the bacillus in vitro.