Macrophages
Different types of macrophages
Macrophages can polarize into different
phenotypes to shape macrophage
response and to cluster them according to
the stimuli. Depending on the diversity of
microenvironmental stimuli, amounts of
cytokines, and duration of exposure,
macrophages counteract these pressures by deploying specific facilities.
Macrophage polarization → phenotype loss, switch of phenotypes, phenotype modulation.
M1-like macrophages (LPS(+IFNγ)) → infection & inflammation (early to mid-stage of infection)
First line of defense against intracellular pathogens and promote Th1 polarization of CD4 cells.
- High level of phagocytic activity
- Contain CD64 and CD80
- Produce proinflammatory cytokines (IL-1β, IL-6, IL-12, IL-18 and IL-23, TNF-α, type I IFN)
- Produce chemokines (CXCL1, CXCL3, CXCL5, CXCL8, CXCL9, … )
- Characterized by microorganisms and matrix debris phagocytosis and high antigen
presentation in early phase.
M2-like macrophages (IL-4) → tissue repair & after inflammation (altered stage of infection)
Involved in parasitic, helminthic, and fungal infections. Induced to Th2 responses.
- Polarized by M-CSF, IL-4, IL-10, IL-13 or a combination.
- Contain CD64, CD209m (C-type lectin)
- Induce cyto- & chemokines (IL-13, IL-1R, CCL1, CCL2, …)
- Can produce IL-8, MCP-1, IP-10, MIP-1β, CCL5, and RANTES to recruit neutrophils,
monocytes, and T lymphocytes in anti-inflammatory or regulatory response.
Subsets
M2a-like → stimulated by IL-4 or IL-13.
- Express high CD86 and CD200R, and low CD14 and TRL4
M2b-like → stimulated by LPS or IL-1β.
- Express high CD80 and CD14, IL-10, CCL1, and proinflammatory cytokine production,
and low HLA-DR expression and IL-12 secretion.
M2c-like → stimulated by IL-10. Prevents tissue inflammation.
- Express high CCL18 and CCL16, CD163, and low CD84 and HLA-DR.
M2d-like / Tumor-associated macrophages (TAMs) → stimulated by IL-6 and M-CSF
- Express high IL-10, and low IL-12 and TGF-β
- Inhibit proinflammatory M1 macrophages, contributes to angiogenesis and tumor
metastasis.
1
,Alternative types
MRs (regulatory macrophages) → produce IL-10 upon LPS stimulation. Induces tolerance of
solid organ transplants and xenoimmune response.
M4 macrophages → induced upon CXCL4 stimulation, express S100A8, mannose receptor
CD206, matrix metalloproteinase 7, and release of IL-6 and TNF-α. Proatherogenic and have a
weak phagocytosis activation.
Mhem macrophages → atheroprotective, heme-dependent activating transcription factor (ATF1)
and CD163 expression. Erythrocyte phagocytosis. Increased cellular iron, reduced oxidative
stress, suppressed inflammatory activation, and increased IL-10 production.
There are no fully M1 or M2 in the body, macrophages constantly sense their surroundings,
expressing both M1 and M2 characteristics.
M1-like macrophages do not switch to M2-
like macrophages (and other way around),
since it is more energy efficient to proliferate
new macrophages from monocytes.
Types of inflammation →
2
,Energy metabolism
Not only energy provision, but also regulate macrophages phenotype and function.
Warburg effect → switching to glycolysis in the presence of oxygen.
M1-like
- Inhanced glycolytic metabolism, impaired OXPHOS. Low amount of ATP (2 per glucose) .
o OXPHOS impaired by NO and itaconate. Electrons flow backwards, driving ROS
production, HIF-1α stabilization, and IL-1β expression.
- iNOS → converts arginine into nitric oxide (NO)
- Pentose Phosphate Pathway (PPP), supports inflammatory response by generating
amino acids for protein synthesis, ribose for nucleotides, NADPH for ROS by NADPH
oxidase, and NO production.
o More info
- Increased synthesis of acetyl-CoA, TCA cycle disruption:
o After citrate → when accumulated converted into acetyl-CoA. Serves as building
block for fatty acid and lipid synthesis, essential for macrophages in
inflammation.
Can be redirected to itaconate by Irg1, which can inhibit ETC in response to LPS,
linking citrate and succinate accumulation.
o After succinate → increased accumulation leads to stabilization of HIF-1α and
induction of IL-1β
- Citrate accumulation for FAS, support inflammatory signaling and NO & TNF production.
- FAO needed for NLRP3 inflammasome activation and IL-1β secretion.
- Uses glucose, taking away the nutrients for bacteria
Glycolysis in M1-like macrophages
M1-like exhibit higher expression of Glut1 compared to M2-like.
HIF-1α mediates upregulation of GLUT1 and other glycolysis-associated genes.
3
, M2-like
- Arginine is metabolized by arginase-1
- Glycolysis is induced and crucial for IL-4-induced macrophage activation.
o IL-4 via AKT and mTROC1 increase glucose metabolism
o Blocking IL-4 diminishes IL-4 induced expression of Arg1, Retnla, and Mgl2
o IL-4 promotes glycose metabolism via mTORC2 and IRF4
- OXPHOS is slower, but more ATP (~30 per glucose)
- TCA cycle intact
Macrophage differentiation
Waves of embryonic hematopoiesis
Fetal macrophages develop before the development of hematopoietic stem cells (HSCs) and are
essential in the concept that macrophages might represent a lineage independent of HSCs.
- 1st wave – primitive hematopoiesis → develops from posterior plate mesoderm in blood
islands of the extra-embryonic yolk sac around E7.0. Giving rise to primitive
erythroblasts, megakaryocytes, and macrophages.
- 2nd wave – transient definitive wave → erythro-myeloid precursors (EMPs) arise from YS
hemogenic endothelium between E8.0 and E8.5. EMPs exhibit erythroid and broad
myeloid potential.
Once blood circulation is established, EMPs migrate into fetal liver (FL), where they
expand and differentiate into cells of multiple lineages, including monocytes.
o Early EMP-like cells → E7.5, give rise to macrophages and might represent
primitive progenitors. Express CSF-1R.
o Late EMP-like cells → E8.25, new wave of hematopoietic progenitors arises from
intraembryonic hemogenic endothelium. Express c-Myb.
o Definitive hematopoiesis → immature HSCs in P-Sp proceeds to give rise to fetal
HSCs at E10.5 in aorta, gonads, and mesonephros regions. These precursors
colonize in FL where they establish definitive hematopoiesis and seed fetal BM
where they will lead to generation of adult BM HSCs.
o From E12.5 the FL becomes the major hematopoietic organ with the embryo and
contains progenitors of different origins and varied potentials, which give rise to
emergent immune system.
The completion of definitive hematopoiesis depends upon c-Myb expression in EMPs. The
expression of c-Myb increases with time.
4
Different types of macrophages
Macrophages can polarize into different
phenotypes to shape macrophage
response and to cluster them according to
the stimuli. Depending on the diversity of
microenvironmental stimuli, amounts of
cytokines, and duration of exposure,
macrophages counteract these pressures by deploying specific facilities.
Macrophage polarization → phenotype loss, switch of phenotypes, phenotype modulation.
M1-like macrophages (LPS(+IFNγ)) → infection & inflammation (early to mid-stage of infection)
First line of defense against intracellular pathogens and promote Th1 polarization of CD4 cells.
- High level of phagocytic activity
- Contain CD64 and CD80
- Produce proinflammatory cytokines (IL-1β, IL-6, IL-12, IL-18 and IL-23, TNF-α, type I IFN)
- Produce chemokines (CXCL1, CXCL3, CXCL5, CXCL8, CXCL9, … )
- Characterized by microorganisms and matrix debris phagocytosis and high antigen
presentation in early phase.
M2-like macrophages (IL-4) → tissue repair & after inflammation (altered stage of infection)
Involved in parasitic, helminthic, and fungal infections. Induced to Th2 responses.
- Polarized by M-CSF, IL-4, IL-10, IL-13 or a combination.
- Contain CD64, CD209m (C-type lectin)
- Induce cyto- & chemokines (IL-13, IL-1R, CCL1, CCL2, …)
- Can produce IL-8, MCP-1, IP-10, MIP-1β, CCL5, and RANTES to recruit neutrophils,
monocytes, and T lymphocytes in anti-inflammatory or regulatory response.
Subsets
M2a-like → stimulated by IL-4 or IL-13.
- Express high CD86 and CD200R, and low CD14 and TRL4
M2b-like → stimulated by LPS or IL-1β.
- Express high CD80 and CD14, IL-10, CCL1, and proinflammatory cytokine production,
and low HLA-DR expression and IL-12 secretion.
M2c-like → stimulated by IL-10. Prevents tissue inflammation.
- Express high CCL18 and CCL16, CD163, and low CD84 and HLA-DR.
M2d-like / Tumor-associated macrophages (TAMs) → stimulated by IL-6 and M-CSF
- Express high IL-10, and low IL-12 and TGF-β
- Inhibit proinflammatory M1 macrophages, contributes to angiogenesis and tumor
metastasis.
1
,Alternative types
MRs (regulatory macrophages) → produce IL-10 upon LPS stimulation. Induces tolerance of
solid organ transplants and xenoimmune response.
M4 macrophages → induced upon CXCL4 stimulation, express S100A8, mannose receptor
CD206, matrix metalloproteinase 7, and release of IL-6 and TNF-α. Proatherogenic and have a
weak phagocytosis activation.
Mhem macrophages → atheroprotective, heme-dependent activating transcription factor (ATF1)
and CD163 expression. Erythrocyte phagocytosis. Increased cellular iron, reduced oxidative
stress, suppressed inflammatory activation, and increased IL-10 production.
There are no fully M1 or M2 in the body, macrophages constantly sense their surroundings,
expressing both M1 and M2 characteristics.
M1-like macrophages do not switch to M2-
like macrophages (and other way around),
since it is more energy efficient to proliferate
new macrophages from monocytes.
Types of inflammation →
2
,Energy metabolism
Not only energy provision, but also regulate macrophages phenotype and function.
Warburg effect → switching to glycolysis in the presence of oxygen.
M1-like
- Inhanced glycolytic metabolism, impaired OXPHOS. Low amount of ATP (2 per glucose) .
o OXPHOS impaired by NO and itaconate. Electrons flow backwards, driving ROS
production, HIF-1α stabilization, and IL-1β expression.
- iNOS → converts arginine into nitric oxide (NO)
- Pentose Phosphate Pathway (PPP), supports inflammatory response by generating
amino acids for protein synthesis, ribose for nucleotides, NADPH for ROS by NADPH
oxidase, and NO production.
o More info
- Increased synthesis of acetyl-CoA, TCA cycle disruption:
o After citrate → when accumulated converted into acetyl-CoA. Serves as building
block for fatty acid and lipid synthesis, essential for macrophages in
inflammation.
Can be redirected to itaconate by Irg1, which can inhibit ETC in response to LPS,
linking citrate and succinate accumulation.
o After succinate → increased accumulation leads to stabilization of HIF-1α and
induction of IL-1β
- Citrate accumulation for FAS, support inflammatory signaling and NO & TNF production.
- FAO needed for NLRP3 inflammasome activation and IL-1β secretion.
- Uses glucose, taking away the nutrients for bacteria
Glycolysis in M1-like macrophages
M1-like exhibit higher expression of Glut1 compared to M2-like.
HIF-1α mediates upregulation of GLUT1 and other glycolysis-associated genes.
3
, M2-like
- Arginine is metabolized by arginase-1
- Glycolysis is induced and crucial for IL-4-induced macrophage activation.
o IL-4 via AKT and mTROC1 increase glucose metabolism
o Blocking IL-4 diminishes IL-4 induced expression of Arg1, Retnla, and Mgl2
o IL-4 promotes glycose metabolism via mTORC2 and IRF4
- OXPHOS is slower, but more ATP (~30 per glucose)
- TCA cycle intact
Macrophage differentiation
Waves of embryonic hematopoiesis
Fetal macrophages develop before the development of hematopoietic stem cells (HSCs) and are
essential in the concept that macrophages might represent a lineage independent of HSCs.
- 1st wave – primitive hematopoiesis → develops from posterior plate mesoderm in blood
islands of the extra-embryonic yolk sac around E7.0. Giving rise to primitive
erythroblasts, megakaryocytes, and macrophages.
- 2nd wave – transient definitive wave → erythro-myeloid precursors (EMPs) arise from YS
hemogenic endothelium between E8.0 and E8.5. EMPs exhibit erythroid and broad
myeloid potential.
Once blood circulation is established, EMPs migrate into fetal liver (FL), where they
expand and differentiate into cells of multiple lineages, including monocytes.
o Early EMP-like cells → E7.5, give rise to macrophages and might represent
primitive progenitors. Express CSF-1R.
o Late EMP-like cells → E8.25, new wave of hematopoietic progenitors arises from
intraembryonic hemogenic endothelium. Express c-Myb.
o Definitive hematopoiesis → immature HSCs in P-Sp proceeds to give rise to fetal
HSCs at E10.5 in aorta, gonads, and mesonephros regions. These precursors
colonize in FL where they establish definitive hematopoiesis and seed fetal BM
where they will lead to generation of adult BM HSCs.
o From E12.5 the FL becomes the major hematopoietic organ with the embryo and
contains progenitors of different origins and varied potentials, which give rise to
emergent immune system.
The completion of definitive hematopoiesis depends upon c-Myb expression in EMPs. The
expression of c-Myb increases with time.
4
