ABSTRACT
NormalHematolymphopoiesis Normalhematolymphoidfunctionrequiresthecontinuousproductionofmature redcells,platelets,andleukocytes(lymphocytes,granulocytes,andmonocytes/ macrophages).Innormaladultsbillionsofmaturecellsareproducedeveryday fromalimitednumberofpluripotentstemcellswhichrepresentonlyaminor populationofbonemarrowcells.Thepoolofstemcellshasthecapabilityof (a)self-renewaland(b)commitmentanddeterminationtocellsofthevarious lineages.Isolationandcharacterizationofsuchstemcellshaslongrepresentedan enigma,butrecentlysubstantialenrichmentofmurineandhumanhematopoietic stemcellshasbeenachieved(1-5).Theproliferationandmaturationofimmature stemcellstotheirmatureprogeniesofthevariouslineagesisunderstrictbut flexiblecontrol,whichincludestheoperationofseveralfeedbackloops.Hematolymphopoiesiscanthusberegulatedatlevelsandcanbemarkedly increasedondemand.Anumberofcytokineshavenowbeenshowntoinfluence hematolymphopoiesisinapositiveornegativeway(6-8).Manyofthese cytokinescanbeproducedbystromalcellsinthebonemarrowand/orbyvarious typesofbloodcells.Undercertaincircumstancesplasmalevelsofvarious cytokinesmaybesufficientlyhighastoinfluencebonemarrowcellsinan endocrinemanner.Theimportanceoftheinteractionofprogenitorcellswith
the past decade the availability of monoclonal antibodies against leukocyte differentiation antigens (CD antigens) has greatly facilitated the precise characterization of different subpopulations of blood cells and has also given rise to an increased knowledge of the various stages of development within the different cell lineages (9-11). This tool has also been of immense help for isolation of various cell populations and for studies of growth and maturation of hematopoietic cells. A schematic drawing of hematolymphoid development is shown in Figure 1.
