Monocytes as Targets for Cancer Therapies

Introduction

They are the largest type of cells in the peripheral blood under normal conditions. Their cytoplasm has azurophillic granules which stain purple to dark blue. They originate from the myeloid or progenitor cells in the bone marrow both during homeostasis as well as inflammation and migrate into blood. The works by (Dunay et al., 2008) and Serbina et al(2006) have thrown some light on the mechanism by which the monocytes leave bone marrow. They have shown that these cells egress from the bone marrow under the influence from CCR2 expressed by Gr-1hi monocytes in mouse (Dunay et al., 2008 and Serbina et al., 2006). The circulating TLR –Ligands can induce the production major monocyte chemoattractant MCP-1 by the bone marrow mesenchymal and progenitor cells (Shi et al., 2011). MCP-1 binds to CCR2 and promotes their egress from the bone marrow. In humans the exact mechanism is still not known. Further the exact mechanism of functioning of Gr1 low (mouse) monocyte subsets is yet to be ascertained. Apart from the bone marrow the spleen has a large reservoir of these cells.