ADHESION MOLECULES IN HEMATOPOIESIS

In the adult mammal, haemopoiesis is restricted to the extravascular c ompartment of the bone marrow (BM) where primitive haemopoietic stem c ells (HSC) and their clonogenic progeny develop in intimate contiguity with a heterogeneous population of stromal cells that comprise the ha emopoietic micro-environment (HM). Although the importance of cellular interactions between primitive haemopoietic progenitor cells (HPC) an d marrow stromal cells is well established, precise definition of the nature of many of these interactions at the molecular level is lacking and remains an objective of fundamental importance to understanding o f haemopoietic regulation. Current data suggest that a wide variety of cell surface molecules representing several adhesion molecule superfa milies, including integrins, selectins, sialomucins and the immunoglob ulin gene superfamily, are involved in supporting cell-cell and cell-e xtracellular matrix (ECM) interactions. These diverse CAM-ligand inter actions, rather than simply serving to initiate and maintain contact b etween HPC and stromal cells and ECM components, also have an addition al, more direct role in controlling the growth and development of prim itive haemopoietic cells.