Spleen-derived macrophages are readily polarized into classically. activated (M1) or alternatively activated (M2) states

Bone marrow derived macrophages (BM-M Phi) that differentiate from precursor cells can be polarized into classically activated pro-inflammatory (M1) or alternatively activated (M2) states depending upon the cytokine microenvironment. We questioned whether tissue M Phi, such as spleen-derived M Phi (Sp-M Phi), have the ability to differentiate into M1 or M2 cells. We show in response to activation with IFN-gamma (IFN-gamma) and lipopolysaccharide (LPS), that the Sp-M Phi readily acquired an M1 status indicated by up-regulation of iNOS mRNA, nitric oxide (NO) production, and the co-stimulatory molecule CD86. Conversely, Sp-M Phi exposed to IL-4 exhibited increased levels of mannose receptor (CD 206), arginase-1 (Arg)-1 mRNA expression, and significant urea production typical of M2 cells. At this stage of differentiation, the M2 Sp-M Phi were more efficient at phagocytosis of cell-associated antigens than their M1 counterparts. This polarization was not indefinite as the cells could revert back to their original state upon the removal of stimuli and exhibited flexibility to convert from M2 to M1. Remarkably, both M1 and M2 Sp-M Phi induced more CD4 expression on their cells surface after stimulation. We also demonstrate that adherent macrophages cultured for a short term in IL-4 enhances ARG-1 and YM-1 mRNA along with increasing urea producing capacity: traits indicative of an M2 phenotype. Moreover, in response to in vivo virus infection, the adherent macrophages obtained from spleens rapidly express iNOS. These results provide new evidence for the polarization capabilities of Sp-M Phi when exposed to pro-inflammatory or anti-inflammatory cytokines. (C) 2014 Elsevier GmbH. All rights reserved.