Aims Colonic inflammation is followed by regeneration supported by bone marrow-derived cells (BMDCs) including multipotent cells. They migrate to the colonic epithelial layer and may transdifferentiate into epithelial-like cells or keep their stem cell characteristics and produce progenies. The aim was to study the role of lymphoid aggregates in the migration and transition of BMDCs in both healthy colons and non-specific colitis (NSC).

Methods Samples of normal colon (n=5) and NSC (n=5) from female patients who were initially transplanted with male bone marrow were studied. After detecting XY chromosomes using fluorescent in situ hybridisation, tissue sections were digitalised, the coverslips were eliminated and the samples were double stained for CD45 and cytokeratin with immunofluorescence. Then CDX2 expression, as a sign of intestinal epithelial commitment of Musashi-1+ stromal BMDCs, was also tested with both immunoperoxidase and parallel immunofluorescence stainings. The slides were digitalised again and analysed simultaneously.

Results A significant increase in intraepithelial CD45–BMDCs was found in regions adjacent to lymphoid aggregates (median: 1.01) compared with healthy epithelial regions (median: 0.0175) or NSC (median: 0.04) samples. The stromal Musashi-1+ cells were positive for CDX2 as well, as a sign of epithelial differentiation. The CDX2+ cells bearing the Y chromosome proved the epithelial commitment of several stromal BMDCs.

Conclusion Elevated number of intraepithelial CD45−BMDCs at lymphoid aggregates suggests that BMDCs play a role in epithelial regeneration and that lymphoid aggregates serve as their migration route.