Subset M1 classical M2a alternative M2b type II M2c deactivated
Function/phenotype        
Stimulation/Differentiation LPS, IFNγ, GM-CSF L-4 / IL-13 IC, LPS, IL-1β IL-10, TGFβ, Glucocorticoids
Cytokine expression TNFα,IL-1b,IL-6,IL-12,IL-18, IL-23, IL-10low IL-12low,IL-23low, TGFβ, IL-10high, IL-1Ra, sIL-1R, II decoy IL-10high,IL-12low, IL-23low, TNFα, IL-1b, IL-6 IL-10high,IL-12low, IL-23low, TGFβ
Chemokine expression CCL2,3,4,5,11,17 & 22 CXCL1,2,3,5,8,9,10, 11 & 16 CCL-17, CCL18, CCL-22, CCL-24 CCL-1 CCL-16, CCL-18 CXCL13
Scavenger Receptor expression - SR, MR - MR, CD163
Signalling STAT-1, STAT-4, SOCS-3 STAT-3 - STAT-6
Tryptophan metabolism iNOS Arg+ iNOS Arg+
Function Anti-microbial Pro-inflammatory Tissue-damage Th1CMI response Anti-Tumoural Anti-parasitic Allergic response Tissue repair Th2 response Anti-parasitic Allergic response Humoral immun. Th2 response Anti-inflammatory Immunoregulation Scavenger Tissue-repair Tumour promotion
Table 1: Macrophage functional phenotypes of defined subsets: M1 classical and M2 alternatively activated phenotypes are characterised according to polarising stimulation/differentiation signals, cytokine and chemokine expression, scavenger/phagocytic receptors, tryptophan metabolism and intracellular signalling molecules. In general iNOS Mφs are M1 and Arg+ Mφs are M2; defining subsets as pro-inflammatory and driving CMI/anti-tumoral responses or anti-inflammato8/ry and driving humoral/regulatory and pro-tumoral responses, respectively. Although M1 classical and M2 alternatively activated subsets are generally acknowledged, no firm evidence exists for the existence of the M2- variants, M2a, M2b and M2c. Note the expression of iNOS by M2b subset; a characteristic more typical of M1 Mφs. It is possible that these additional subsets may represent intermediates between M1 and M2 Mφs. This table has been adapted from [8,10,18,46,80].