cytokines, including TNF, IL18, IL-12 and IL-23, which mediate 
immune reactions in several chronic inflammatory and autoimmune diseases, including rheumatoid arthritis, Crohn’s disease, multiple sclerosis and autoimmune hepatitis. M2 macrophages, in contrast, inhibit the production of a wide variety of pro-inflammatory mediators, such PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19729111 as IL-10, and regulate wound healing. Thus, targeted depletion of M1 and boosting the activities of M2 macrophages are emerging as an attractive combined therapeutic strategy for autoimmune diseases. Better understanding of the MedChemExpress AVE-8062 mechanisms that regulate M1/M2 differentiation should improve these therapeutic approaches and could lead to reduced joint destruction in inflammatory arthritides. Granulocyte macrophage-colony stimulating factor drives myeloid progenitor differentiation into granulocytes and M1 monocyte/macrophages with a pro-inflammatory cytokine profile and also into cells with dendritic cell properties, and thus it is often employed in studies of DC development and function. However, GM-CSF is not critical for macrophage development since mice lacking GM-CSF do not have notable defects in tissue macrophages. In contrast, targeted ablation of M-CSF or its receptor causes severe depletion of macrophages in many tissues associated with failure of osteoclast formation and osteopetrosis, indicating that M-CSF plays a major role in the generation of macrophages. Macrophages induced in response to M-CSF alone have an anti-inflammatory cytokine profile and are similar to M2 macrophages. In general, M2 macrophages switch to a M1 phenotype in response to IFN- and LPS and secrete large amounts of cytokines involved in autoimmune responses. We previously reported that TNF increases CD11b+Gr-1-/lo OCP numbers by stimulating expression of the M-CSF receptor, cfms, which has important roles in OCP proliferation, OC formation and survival. However, it was not known if these are M1 PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19730426 or M2 macrophages or if the positive or negative regulatory effects of TNF on OC formation involve modulation of M1/M2 differentiation. Here, we have shown that TNF promotes a switch of M-CSF-induced F4/80+CD11b+Ly6C-Gr1- M2 to F4/80+CD11b+Ly6C+Gr1- and F4/80+CD11b+Ly6C-Gr1-CD11c+ M1 macrophages based on our findings that: 1) the Ly6C+ Gr1- cells comprise 5063% of CD11b+F4/80+ from T-OCPs and only 1725% from M-OCPs; and in contrast, Ly6C-Gr1- cells comprise 34 47% of the CD11b+F4/80+ T-OCPs compared to 6778% of these cells from M-OCPs; 2) CD11c+ cells in both Ly6C+Gr1- and Ly6C-Gr1- populations from T-OCPs are also increased compared to the respective populations from M-OCPs; and 3) importantly, Ly6C+Gr1- cells from both M- and T-OCPs have increased expression of the M1 marker genes, iNOS, TNF, IL-1 and TGF1, compared to Ly6C- Gr1- cells. Ly6C-Gr1- 15 / 20 TNF Induced Osteoclast Formation cells from T-OCPs also have increased expression of iNOS and TGF1 compared to those from M-OCPs, and both Ly6C+Gr1- and Ly6C-Gr1- cells from T-OCPs have decreased expression of the M2 genes, IL-10 and PPAR-. A switch from a M2 to a M1 phenotype can also change the OC forming potential of these cells. For example, Raw264.7 cells, a murine macrophage cell line that can differentiate into OCs in response to RANKL without the need to add M-CSF, have enhanced OC forming potential when they are induced to a M1 phenotype by IFN- and LPS. We found that only Ly6C+Gr1- M1 cells, but not Ly6C-Gr1- M2 cells in the CD11b+F4/80+ population from M-OCPs formed OCs
