Table 1.

Macrophage polarization in OA and cartilage regeneration.

Macrophage polarization	Stimuli	Transcription factors	Phenotype	Released products	Functional roles	Potential tools for OA treatment
M1	IFN-g, LPS, TNF-a	IRF1, IRF5, IRF8, Pu.1, STAT1, STAT2, NFkB	CD80, CD86, CD40, MHC-II	TNF-a, IL-1b, IL-6, IL-12, IL-23, OSM, NO, CXCL10, IL-8, CCL5, CXCL9, CXCL11, MMP1, MMP3, MMP9, MMP13, ADAMTS	Inflammation, type 1 response and tissue injury microbicidal. → OA induction.	M1 blocker** Depletion of CD14+ Macrophages**
M2	IL-4, IL-13, IL-10 and TLRs agonists, MSCs (?)	IRF4, Pu.1, SOCS1, STAT6, JMJD3, PPARg, PPARd, GATA3, C/EBPb	ARG-1, CD163, CD206	IL-10, IL-1RA, TGF-b, IGF, CCL18, CCL4, CCL13, CCL17, MMP1, MMP12	Anti-inflammatory response, type 2 response, tissue repair, chondrogeneic and turnover of extracellular matrix. → Cartilage regeneration.	M2 inducers: oxLDL, collagen type II, MSCs*. Blocking mTOR pathway?**

^*The M2 polarization can be halt by the microenvironment.

^**Further studies are required.

OA, osteoarthritis.

Bold is used to highlight information.