Microbiology of the intestinal lymph follicle: a clue to elucidate causative microbial agent(s) in Crohn's disease

Clinicopathological and Ileocolonoscopic Characteristics in Patients with Nodular Lymphoid Hyperplasia in the Terminal Ileum

Nodular lymphoid hyperplasia (NLH) in the small intestine is a rare benign lesion, characterized by the presence of multiple small nodules on the surface of the intestine. To define the clinicopathological and colonoscopic characteristics in Chinese patients with ileal NLH, we collected 65 patients with NLH in the terminal ileum from the endoscopic database in our hospital and clinical data from medical records. Histology and immunohistochemical staining were performed in the biopsies. The results demonstrated that the main symptoms included diarrhea (70.8%), abdominal pain (60.0%), hematochezia (46.2%), anemia (40.0%), and hypoproteinemia (21.5%). Enteroscopy revealed multiple, sporadic, granular or round-shaped nodules with diameters between 2 and 5 mm in the terminal ileum. The histology revealed the nodules consisted of mass lymphoid follicles in the lamina propria and submucosa of the terminal ileum. The follicles contained mitotically active germinal centers surrounded by well-defined lymphocyte mantles and composed predominantly of CD20⁺ B cells. The diseases found in patients with NLH included chronic diarrhea, Crohn's disease, ischemic enterocolitis and allergic purpura. The level of hemoglobin in NLH patients who had diarrhea and hematochezia remarkably decreased as compared with those in patients with chronic diarrhea. In conclusion, ileocolonoscopic screening is an important step to find the NLH in terminal ileum patients with diarrhea, abdominal pain, hematochezia, and hypoproteinemia. Histological examination is necessary for the exclusion of malignancy and chronic inflammation.

Validation of 16S rDNA sequencing in microdissected bowel biopsies from Crohn's disease patients to assess bacterial flora diversity

The bowel flora is implicated in Crohn's disease (CD) pathogenesis but its precise role is still unclear. Several non-mutually exclusive hypotheses have been proposed: an unidentified persistent pathogen; excessive bacterial translocation; an immune system abnormality in response to normal bacteria; or a breakdown in the balance between protective and harmful bacteria. These hypotheses can be tested by identifying bacteria in specific microscopic bowel structures or lesions. The present paper describes a novel technique to assess bacterial flora diversity in bowel biopsies, by combining laser capture microdissection with broad-range 16S rDNA sequencing. Fifty-four samples comprising histologically normal and pathological mucosa, MALT, ulcers, submucosal lymphangiectasias, epithelioid granulomas, and lymph nodes were microdissected out of 30 bowel biopsies from five CD patients. Bacterial 16S rDNA was successfully amplified by PCR in all samples, and PCR products from 15 samples were selected for cloning and sequence analysis. A total of 729 bacterial DNA sequences were analysed, which could be attributed to six different phyla (Proteobacteria, Firmicutes, Bacteroidetes, Actinobacteria, Fusobacteria, and Planctomycetes). DNA from typical bowel bacteria (Enterobacteriaceae, Clostridiales, Bacteroidetes, Fusobacteria) was detected in all microdissected areas. It was thus convincingly demonstrated that 16S rDNA sequencing can be combined with microdissection to study the bowel flora. However, no specific persistent pathogen causal for CD was identified. The results suggest that Enterobacteriaceae may initiate or colonize ulcers in CD. Translocation of bacteria through established mucosal lesions or as a result of increased permeability may be involved in the evolution towards chronic inflammation and in the establishment of persistent lesions. Further study is needed to confirm these preliminary findings.

Endoscopic identification of Peyer’s patches of the terminal ileum in a patient with Crohn’s disease

We presented a 20-year-old patient with Crohn’s disease (CD). Colonoscopy revealed longitudinal ulceration in the terminal ileum and rectal aphtoid ulcers. After treatment with mesalamine and total parenteral nutrition, repeat colonoscopy revealed a granular elevated area in the terminal ileum, which appeared as an irregular dome-like elevation with irregularly arranged villi on magnifying endoscopy. Biopsy specimens taken from the region showed microgranulomas and lymphoid hyperplasia. Scanning electron microscopy revealed the presence of M cells, confirming that the area corresponded to Peyer’s patches. Peyer’s patches by magnifying endoscopy and electron microscopy may provide insights into the pathogenesis of CD.

Presence of bacterial 16S ribosomal RNA gene segments in human intestinal lymph follicles

BACKGROUND

There is currently no information regarding microbial agents inside the intestinal lymph follicles.

METHODS

Biopsy or resected specimens, mostly from macroscopically normal areas, were sectioned with a cryostat. DNA was extracted from microdissected samples, exclusively from the lymph follicle. Amplification of DNA was performed using universal primers designed from conserved regions of bacterial 16S ribosomal RNA (rRNA). Several clones with inserts of around 400 base pairs were subjected to DNA sequence analysis followed by a database homology search.

RESULTS

Bacterial 16S rRNA gene segments were detected in the lymph follicle in 2 of 14 (14%) non-inflammatory bowel disease (IBD) cases, 4 of 14 (28%) Crohn disease cases, and in 2 of 5 (40%) ulcerative colitis cases. Nineteen 16S rRNA gene segments were recognized in the eight positive cases. Five segments showed 100% identity to known bacterial 16S rRNAs, namely staphylococcus species, Streptococcus sanguis, and Paracoccus marcusii. However, the other 14 segments showed below 100% identity, indicating either the presence of unknown bacteria or of bacteria without known DNA data. No single identified or unidentified bacterium, characteristic of IBD, including Mycobacterium paratuberculosis and Listeria monocytogenes, was detected.

CONCLUSIONS

The present study confirms the presence of bacterial 16S rRNA gene segments in human intestinal lymph follicles and paves the way for new investigations into the microbiology of the lymph follicle. Whether or not bacteria inside the lymph follicle is a primary stimulus in IBD has yet to be clarified.