The mesenchymal elements of the intestinal lamina propria reviewed here are the myofibroblasts, fibroblasts, mural cells (pericytes) of the vasculature, bone marrow–derived stromal stem cells, smooth muscle of the muscularis mucosae, and smooth muscle surrounding the lymphatic lacteals. These cells share similar marker molecules, origins, and coordinated biological functions previously ascribed solely to subepithelial myofibroblasts. We review the functional anatomy of intestinal mesenchymal cells and describe what is known about their origin in the embryo and their replacement in adults. As part of their putative role in intestinal mucosal morphogenesis, we consider the intestinal stem cell niche. Lastly, we review emerging information about myofibroblasts as nonprofessional immune cells that may be important as an alarm system for the gut and as a participant in peripheral immune tolerance.

The subepithelial intestinal myofibroblast is an important cell orchestrating many diverse functions in the intestine and is involved in growth and repair, tumorigenesis, inflammation, and fibrosis. The myofibroblast is but one of several α-smooth muscle actin-positive (α-SMA(+)) mesenchymal cells present within the intestinal lamina propria, including vascular pericytes, bone marrow-derived stem cells (mesenchymal stem cells or hematopoietic stem cells), muscularis mucosae, and the lymphatic pericytes (colon) and organized smooth muscle (small intestine) associated with the lymphatic lacteals. These other mesenchymal cells perform many of the functions previously attributed to subepithelial myofibroblasts. This review discusses the definition of a myofibroblast and reconsiders whether the α-SMA(+) subepithelial cells in the intestine are myofibroblasts or other types of mesenchymal cells, i.e., pericytes. Current information about specific, or not so specific, molecular markers of lamina propria mesenchymal cells is reviewed, as well as the origins of intestinal myofibroblasts and pericytes in the intestinal lamina propria and their replenishment after injury. Current concepts and research on stem cell therapy for intestinal inflammation are summarized. Information about the stem cell origin of intestinal stromal cells may inform future stem cell therapies to treat human inflammatory bowel disease (IBD).

Probiotics based on Bacillus strains have been increasingly proposed for prophylactic and therapeutic use against several gastro-intestinal diseases. We studied safety for two Bacillus strains included in a popular East European probiotic. Bacillus subtilis strain that was sensitive to all antibiotics listed by the European Food Safety Authority. Bacillus licheniformis strain was resistant to chloramphenicol and clindamycin. Both were non-hemolytic and did not produce Hbl or Nhe enterotoxins. No bceT and cytK toxin genes were found. Study of acute toxicity in BALB/c mice demonstrated no treatment-related deaths. The oral LD(50) for both strains was more than 2 x 10(11) CFU. Chronic toxicity studies were performed on mice, rabbits, and pigs and showed no signs of toxicity or histological changes in either organs or tissues. We demonstrated that while certain risks may exist for the B. licheniformis strain considering antibiotic resistance, B. subtilis strain may be considered as non-pathogenic and safe for human consumption.

The non-white blood cell mesenchymal elements of the intestinal lamina propria are the myofibroblasts, fibroblasts, pericytes, stromal stem cells, muscularis mucosae, and the smooth muscle of the villus core associated with the lymphatic lacteal. We review the functional anatomy of these mesenchymal cells, what is known about their origin in the embryo and their replacement in adults, their putative role in intestinal mucosal morphogenesis, and the intestinal stem cell niche, and we consider new information about myofibroblasts as nonprofessional immune cells. Although our knowledge of the function of mesenchymal cells in intestinal disease is rudimentary, we briefly consider here their roles in cancer and intestinal inflammation.