In vivo detection of mucosal healing-involved histiocytes by confocal laser endomicroscopy.

Histiocytes have a pivotal role in wound repair and intestinal epithelial recovery - the most important goal to sustain gut functionality. Yet, an in vivo description of colonic histiocytes by confocal laser endomicroscopy (CLE) is missing. Here, we report the case of a 45-years-old male patient who was referred to our clinic with weight loss and a history of two consecutive Clostridium difficile colitis episodes, the latter cured 3 wk before present admission. Stool microbiology was negative. Conventional colonoscopy showed atrophy and a light mucosal oedema in the distal colon. During on-going endoscopy, we performed a fluorescein-aided CLE which revealed large polygonal (histiocytes-like) cells with copious cytoplasm and large nuclei in the lamina propria of the sigmoid colon as well as regenerative epithelial changes. Histopathological assessment of biopsies from the same areas confirmed the endomicroscopical findings: Periodic acid-Schiff- and CD68-positive foamy histiocytes in the colonic lamina propria and an advanced epithelial recovery. Since stool microbiology was repeatedly negative and polymerase chain reaction-analysis from colonic biopsies could not detect any mRNA for Thropheryma whippleii and common pathogens, we interpreted this particular setting as a mucosal healing process after consecutive Clostridium difficile infections. In conclusion, by describing these colonic histiocytes, we highlight the clinical usefulness of CLE in describing the entity of histiocytes in vivo and in real-time during the process of post-infectious mucosal healing in the colon.