Haematopoetic Stem Cells in the Adult Human Intestine

Stem cells resident in the small intestinal crypts constantly give rise to epithelial cells of the villi. The small intestine is also recognized as a site of lymphoid development in mice. It is also possible that haematopoetic stem cells are present in the adult human intestine which give rise to lymphoid cells. Detection of recombinase activating gene (RAG) transcripts and IL-7 and IL-15 in the human intestine supports this hypothesis. In this study, multi-parameter flow cytometry was used to detect and characterise hematopoetic stem cells (CD34+ CD45+) in the epithelium and lamina propria of human small intestine. Biopsies and blood were taken from non-diseased patients (n=12) and patients with coeliac disease (n=8). The ratio of lymphocytes to epithelial cells yielded by the biopsies was significantly higher in coeliac patients (p=0.001). Hematopoetic stem cells (HSCs) were detected in the epithelium and lamina propria of all samples at levels significantly higher than peripheral blood (p<0.05). There were significantly more HSCs in the lamina propria than the epithelium of normal patients (p<0.05). Levels of HSCs in the epithelial layer of the coeliac patients were significantly lower than that in normal patients (p=0.02). This is the first demonstration of hematopoetic stem cells in the human small intestine, which, along with the RAG, IL-7 and IL-15 data, supports the hypothesis that lymphoid cells are developing locally.