Enrichment of c-kit+ Lin- haemopoietic progenitor cells that commit themselves to extrathymic T cells in in vitro culture of appendix mononuclear cells

Extramedullary hematopoiesis mimicking acute appendicitis: a rare complication of idiopathic myelofibrosis

Extramedullary hematopoiesis (EMH) is rarely found in the gastrointestinal tract. To our knowledge, EMH involving the appendix was not described. We report a case with a previous history of idiopathic myelofibrosis, which presented with clinical findings of acute appendicitis that necessitate appendectomy after the relief of his anemia. Microscopic examination and immunohistochemistry revealed foci of EMH throughout the mucosa and the submucosa. In the latter, small clusters of hematopoietic cells were also detected in a few dilated vascular structures. The histopathological features of acute appendicitis were not observed. Our case supports that EMH might develop in organs that are not involved in hematopoiesis. Although in gastrointestinal system, obstruction and bleeding are the most common symptomatic manifestations, this case emphasizes that EMH might also present clinically as acute appendicitis. The absence of histopathological features of acute appendicitis raises the possibility that local production of some mediators from hematopoietic precursor cells might contribute to this clinical presentation.

Isolation of mesenchymal stem cells from human vermiform appendix

BACKGROUND

Recent findings have shown that pluripotent stem cells exist in areas outside the bone marrow (BM). Moreover, it has been demonstrated that the appendix is important for the development of mucosal gut immunity, and hematopoietic progenitors have been isolated from animal and human appendices.

MATERIALS AND METHODS

Non-inflamed appendices removed during laparotomy were processed and cultured until the appearance of adherent cells. Differentiations (performed under osteogenic, adipogenic, and myogenic conditions) were confirmed by immunohistochemistry and cytochemistry. Polymerase chain reaction and cytofluorimetric analyses were performed to evidence the presence of genes and protein specific lineages in appendix-derived mesenchymal stem cells (ADMCs).

RESULTS

ADMCs were present in non-inflamed appendices. ADMCs under osteogenic conditions differentiated in osteoblasts and showed increased alkaline phosphatase expression; at the gene level, we observed the expression of Core binding factor alpha 1 (Cbfa1) and osteocalcin in osteogenic induced ADMCs. Under adipogenic conditions, lipidic drops in the cytoplasm, expression of lipoprotein lipase (LpL), and peroxisome proliferator-activated receptor gamma were observed; under myogenic conditions, myotubes expressing muscle specific proteins like desmin were formed. Myogenic regulatory factor 4 and MyoD were selectively induced in the ADMCs under myogenic conditions.

CONCLUSIONS

This study shows for the first time that mesenchymal stem cells can be isolated from normal appendices obtained from a pediatric and adult age group (0-18 years of age). This finding not only may further knowledge of the maturation of the intestinal immunesystem but also could indicate a new physiological role of the human vermiform appendix.

Variant isoforms of CD44 are required in early thymocyte development

The earliest T cells homing to the thymus (CD3-CD4loCD8-) express CD117 (c-kit), CD43 (leukosialin), and the integrins CD11a (alphaL), CD11b (alphaM), CD29 (beta1), CD49f (alpha6), and CD44. Using reagents specific for CD44 variant isoforms (CD44v), we demonstrated that CD44v were expressed on virtually all early thymocytes,whereas cells carrying only the standard molecule (CD44s, not containing any variant domains), which is ubiquitously found on mature lymphocytes later, are very sparse. The expression of CD44v was closely correlated with CD43 and CD117 and was restricted to the CD3-CD4loCD8- stage. CD44v were detected on lymphocyte progenitor populations in the fetal blood, liver, thymus and spleen, as well as in the adult bone marrow. Functional studies demonstrated that only cells expressing CD44v from fetal liver and adult bone marrow could efficiently populate fetal thymic stroma and develop into mature T cells. In fetal thymic organ cultures anti-CD44v antibodies specifically blocked thymocyte development. We also present evidence that CD44v were required for the initial interaction of hematopoietic progenitor cells with the thymic stroma. Our data imply that CD44v are not only a useful marker for hematopoietic progenitors, but also play a functional role in the initiation of thymocyte development.