%0 Journal Article
%T Hematopoietic Stem and Progenitor Cells as Effectors in Innate Immunity
%A Jennifer L. Granick
%A Scott I. Simon
%A Dori L. Borjesson
%J Bone Marrow Research
%D 2012
%I Hindawi Publishing Corporation
%R 10.1155/2012/165107
%X Recent research has shed light on novel functions of hematopoietic stem and progenitor cells (HSPC). While they are critical for maintenance and replenishment of blood cells in the bone marrow, these cells are not limited to the bone marrow compartment and function beyond their role in hematopoiesis. HSPC can leave bone marrow and circulate in peripheral blood and lymph, a process often manipulated therapeutically for the purpose of transplantation. Additionally, these cells preferentially home to extramedullary sites of inflammation where they can differentiate to more mature effector cells. HSPC are susceptible to various pathogens, though they may participate in the innate immune response without being directly infected. They express pattern recognition receptors for detection of endogenous and exogenous danger-associated molecular patterns and respond not only by the formation of daughter cells but can themselves secrete powerful cytokines. This paper summarizes the functional and phenotypic characterization of HSPC, their niche within and outside of the bone marrow, and what is known regarding their role in the innate immune response. 1. Introduction Hematopoietic stem cells (HSC) maintain and replenish all blood cell types in the bone marrow and respond to changing needs for blood cells in peripheral tissues. They give rise to multipotent (produce most blood cell subsets), oligopotent (lymphoid or myeloid restricted), and unipotent hematopoietic progenitor cells (HPC), the latter type restricted to proliferation into a single set of mature blood cells. Throughout embryonic and fetal development, there are multiple sequential sites of hematopoiesis. Though primitive HSC form nucleated red blood cells in the yolk sac, the first definitive HSC appear in the aorta-gonad-mesonephros (AGM) and expand in the fetal liver before finding their niche in the bone marrow (and spleen in rodents) [1, 2]. In adult life, hematopoietic stem and progenitor cells (HSPC) primarily reside in the bone marrow, though recent work has shown that they circulate in blood and lymph and traffic to other hematopoietic and nonhematopoietic organs during homeostasis and stress [3¨C6]. This roving nature of adult HSPC should not be surprising when one considers the changing location of hematopoiesis throughout HSPC ontogeny. Additionally, extramedullary hematopoiesis is well described in the adult and typically occurs at sites of prenatal hematopoiesis [7]. Given the ability of HSPC to leave the bone marrow and circulate in the periphery, that they express pattern recognition
%U http://www.hindawi.com/journals/bmr/2012/165107/