title: Aging of the hematopoietic system.
abstract: OBJECTIVE
  Aging of the hematopoietic system is associated with myeloid malignancies, anemia and immune dysfunction. As hematopoietic stem cells (HSCs) generate all cells of the hematopoietic system, age-associated changes in HSCs may underlie many features of the aged hematopoietic system. Recent findings on age-associated changes in HSCs are reviewed here.
  
  
  RESULTS
  Aged HSCs are myeloid biased, have acquired DNA damage and are functionally compromised. However, overall function of the HSC compartment is well maintained through age-associated expansion of HSCs. Many age-related changes in the hematopoietic system, in particular the clonal myeloid bias of HSCs and the decrease in B and T-cell development, in fact begin during development. Furthermore, HSCs possess specific protective mechanisms aimed at maintaining their number, even at the expense of accumulating damaged cells.
  
  
  CONCLUSIONS
  We argue that age-related changes in HSCs and in the hematopoietic system may not entirely be due to a degenerative aging process, but are the result of developmental and stem cell-protective mechanisms aimed at maximizing fitness during reproductive life. These mechanisms may be disadvantageous later in life as damaged HSCs accumulate and establishment of responses to neoantigens becomes compromised because of the reduced generation of naive T and B cells.
authors.affiliation: Columbia Center for Translational Immunology, Columbia University Medical Center, New York, NY 10032, USA. hs2680@columbia.edu
authors.forename: Hans-Willem
authors.initials: HW
authors.lastname: Snoeck
mesh_terms: D000375:Aging / Q000502:physiology*; D002452:Cell Count; D002454:Cell Differentiation / Q000502:physiology; D049109:Cell Proliferation; D016922:Cellular Senescence / Q000502:physiology; D006410:Hematopoiesis / Q000502:physiology*; D006412:Hematopoietic Stem Cells / Q000502:physiology*; D006801:Humans