Chemokines and their receptors in hematopoietic cell development and functioning

Chemokines play indispensable roles in the hematopoietic system. Most of all, chemokines regulate the migration of hematopoietic cells into various tissue sites and organs by inducing chemotaxis and activating integrins. The positioning of hematopoietic cells in appropriate tissue environments is critical for normal hematopoiesis, which is the process by which immune cells, red blood cells, and platelets are generated. Chemokines regulate the migration of primitive hematopoietic stem and progenitor cells to the bone marrow and the migration of T-cell progenitors to the thymus. They also play important roles in the recruitment and retention of B-cell progenitors in the bone marrow. Ordered migration of T-cells and B-cells to secondary lymphoid tissues, upon completion of their development in the thymus and bone marrow, respectively, is also regulated, in part, by chemokines. Many chemokines have been discovered, because they are induced in inflammatory conditions during infection or injury. After chemokines are induced, they recruit appropriate immune cells to clear pathogens and repair tissue damages. Chemokines also have other functions, such as regulating cell proliferation/cycling, survival/apoptosis, and cell differentiation. In this chapter, I will review the functions of chemokines in the biology of hematopoietic stem/progenitor cells, T-cells, and B-cells. © 2005 Elsevier Inc. All rights reserved.