ABSTRACT
In this chapter, the authors focus on four very different aspects of the immune system that are either totally independent of hematopoietic stem cells (HSC) or involve stem cell properties at the bottom rather than the top of the hematopoietic hierarchy. First, they look at effector cells involved in aspects of the immune response that appear to arise early in development independently of HSC. Second, the authors discuss various cells of the immune response that have the capacity of memory, which at least at first sight seems to recall elements of stem cell behavior. Then they consider what are perhaps more conventional tissue-specific stem cells that support the so-called secondary lymphoid organs in which many aspects of immune responses occur. Lastly, the authors describe the other face of mesenchymal stem cells, that is, how they are able to moderate the effector cells of the immune system.
