Macrophages are a common phagocytic cell and a member of immune cells. It is a white blood cell located in a tissue derived from monocytes. It is characterized by plasticity and versatility. It plays an important role in clearing senescent or apoptotic cells, phagocytosis of immune-related complexes and pathogens, and maintenance of homeostasis. The phenotype and function of macrophages may be polarized by microenvironment.
Figure 1 The plasticity of macrophage
2. Two Sides of Macrophage Function
3. Transcription Factors and Signaling Pathways that Affect Macrophage Polarization
According to the activation state and functions of macrophages, they can be divided into M1-type (classically activated macrophage) and M2-type (alternatively activated macrophage) [1] [2].
IFN-γ can differentiate macrophages into M1 macrophages that promote inflammation. Unlike IFN-γ, IL-4 produced by Th2 cells [3] can convert macrophages into M2-type macrophages that inhibit inflammation.
The role of M1 macrophages is to secrete pro-inflammatory cytokines and chemokines, present antigens, and thus participate in the positive immune response and function as an immune monitor. The main pro-inflammatory cytokines it produces are IL-6, IL-12 and TNF-alpha.
M2 macrophages mainly secrete Arginase-I, IL-10 [4] [5] and TGF-β and other anti-inflammatory cytokines, which have the function of reducing inflammation and contributing to tumor growth and Immunosuppressive function [6]. It plays an important role in wound healing and tissue repair.
In a word, macrophages are a "double-edged sword", which can not only stop the spread of cancer cells, but also help the growth and spread of cancer cells. Macrophages can modulate their activation state from M1 to M2 (or vice versa) based on specific signals in their microenvironment, allowing them to adapt to the changing immune response needs [7].
Figure 2 The type of macrophages
Positive Effects of Macrophages on Tumor Killing: Activated macrophages produce TNF, hydrolyzed proteases, interferons and peroxides to directly kill or inhibit tumor cell growth. Activated macrophages secrete IL-1 and activate T cells to produce various anti-tumor cytotoxic lymphocytes, which can directly kill tumors, or cooperate with macrophages to kill tumors through activated LAK cells, tumor infiltrating lymphocytes or NK cells.
Macrophages Promote Tumor Growth and Metastasis: The mechanism by which macrophages promote tumor growth and metastasis is that macrophages produce tumor growth promoting substances, such as tumor vascular growth factor, human tumor monoclonal cell growth factor and some enzymes and activators, which can respectively lead to tumor angiogenesis and promote tumor cell expansion
On the other hand, enzymes secreted by macrophages destroy the tissues surrounding the tumor, facilitating the proliferation and metastasis of tumor cells. Malignant transformation of macrophages also leads to tumor metastasis.
The phenotype and functional polarization of macrophages are regulated by many factors. Signal transducers and transcriptional activators that affect macrophage polarization are as follows: STATs, interfering regulatory factors (IRFs), nuclear factors (NF-kappab), activating proteins (AP1), peroxisome proliferators activating receptors (PPAR-gamma), and cAMP response element binding protein (CREB). They interact with each other to regulate the phenotype of macrophages.
Figure 3 Factors affecting macrophage polarization
The Notch pathway regulates macrophage polarization by controlling gene expression, thereby modulating the immune response.
Myelo-derived macrophages activate Notch1 and NF-kappab under the stimulation of LPS and toll-like receptors, thus polarized M1-type macrophages. One molecular mechanism of Notch1-dependent M1 polarization is the transactivation of the M1 type gene by NICD1, resulting in the effect of Notch1 activation [8]. In addition, IRF5 is associated with M1 macrophage polarization and can be stimulated by inflammation in atherosclerosis [9], and nitrification of IRF5 protein leads to inhibition of IRF5-targeted M1 macrophage signaling gene activation [10].
The JAK-STAT signaling pathway is also closely related to the phenotypic activity of macrophages [11]. IFN (interferon) works through this signaling pathway. IFN-γ can induce polarization of M1 macrophages. The role of IFN-α/IFN-β-mediated signaling pathways in macrophage polarization is not well understood, but it is known to enhance anti-inflammatory effects under certain conditions.
PI3K pathway plays an important role in the survival of macrophages [12]. Different AKt kinases have different effects on macrophage polarization. Among them, AKt1 can be activated by PI3K, and the ablation of AKt1 leads to polarization of M1-type macrophages, while the ablation of AKt2 leads to polarization of M2-type macrophages [13][14].
In addition to the above signaling pathways, mitochondrial biosynthesis also plays an important role in macrophage polarization [15]. In addition, HGF promotes the transformation of macrophages from M1 to M2 by activating the JAK2/STAT3 signaling pathway. But its molecular mechanism is not clear.
CD68 and CD11b are total markers of macrophages. For M1 and M2 macrophages, they have specific markers.
M1 can choose CD80, CD86, CD64, CD16 and CD32 as markers. In addition, the expression of nitric oxide synthase (iNOS) in M1 can also serve as phenotypic markers.
CD80, also known as B7, B7.1, or BB1, is a T lymphocyte activated antigen. It has a molecular weight of 60 kD. It synergizes with CD86 to activate T lymphocytes and plays an important role in autoimmune monitoring, humoral immune response and transplantation response.
CD86, also known as B7.2, is a T lymphocyte activation antigen with a molecular weight of 80 kD and can be expressed in dendritic cells, monocytes, T lymphocytes and B lymphocytes. CD86 interacts with its ligands CD28 and CTLA4 to induce T lymphocyte proliferation and produce IL-2.
CD64, also known as high affinity immunoglobulin gamma Fc receptor Ⅰ, it has the functions of innate immune response and adaptive immune response.
CD32 is also known as Low affinity immunoglobulin gamma Fc region receptor Ⅱ-b, which is involved in the phagocytosis of immune complexes and the regulation of b cells on the production of antibodies.
CD163 and CD206 are major markers for the identification of M2 macrophages [16] [17] [18]. Related surface markers for M2-type cells also contain CD68. Compared with marker CD68, CD163 is more selective to macrophages, so CD163 can be used as a highly specific marker for M2-type macrophages [19].
In addition, arginase 1 (Arg1) [20] and DECTIN-1 are also ideal phenotypic indicators for the identification of M2 macrophages.
Studies have also shown that FIZZ1, Ym1 and Ly6C [21] [22] can also be used as surface markers associated with M1 or M2 macrophage subpopulations.
CD206, the mannose receptor 1, is a C-type lectin mainly present in macrophages and immature DC cells. It promotes macrophage activation, antigen presentation and immune response [23].
CD163 is a highly specific M2-type tumor-associated macrophage marker expressed primarily on the surface of monocytes and macrophages. CD163 belongs to the class B family of cysteine receptor cysteine-rich (SRCR). It is expressed only in the mononuclear-macrophage cell line.
CD163 can not only resist inflammation, but also play an important role in tumor proliferation and metastasis as a member of tumor-related macrophage family. Studies have shown that CD163 is closely related to breast cancer, bladder cancer, lung cancer, colorectal cancer and other malignant tumors [24]. The infiltration degree of CD163 affects tumor proliferation, invasion, metastasis and prognosis.
CD68 is involved in the phagocytic activity of macrophages. Rapid recirculation of CD68 from endosomes and lysosomes to the plasma membrane may allow the identification over selectin-bearing substrates or other cells.
Recent studies have shown that MS4A4A is expressed only in myeloid cells and is differentially regulated in monocyte-derived M1 and M2 macrophages [25], which can be used as a marker to distinguish between M1 and M2 macrophages.
In the most distinct genes in M1 or M2 macrophages, CD38, Gpr18 and Fpr2 were new M1 markers, and Egr2 and C-MYC were M2 markers. Flow cytometry based on CD38/Egr2 can distinguish M1 and M2 macrophages, and has advantages over classical iNOS, arginase-1 and CD206 phenotype markers [26].
Macrophages are involved in the elimination of pathogens in tissues. When activated, macrophages can engulf and kill pathogenic microorganisms, release pro-inflammatory factors, and collect and activate lymphocytes to induce an adaptive immune response.
Abnormal function of macrophages can lead to a variety of diseases. M1 type macrophages are not only associated with infectious diseases and inflammatory diseases, but also with metabolic diseases such as arteriosclerosis and insulin resistance. M2 macrophages are also associated with the development of a variety of diseases.
Macrophages are functionally heterogeneous in atherosclerosis (As), which promotes inflammation and is involved in the relief of atherosclerosis and the repair of lesions.
Measured by its binding ability in a functional ELISA. Immobilized Human IL17A at 2 μg/ml can bind Anti-IL17A recombinant antibody (CSB-RA624104MA1HU), the EC50 is 1.818-2.170 ng/mL.
Measured by its binding ability in a functional ELISA. Immobilized Human IL6 at 2μg/mL can bind Anti-IL6 recombinant antibody (CSB-RA011664MA1HU),the EC50 is 35.80-41.82 ng/mL
Overlay histogram showing Raw264.7 cells stained with CSB-RA801238A0HU (red line) at 1:50.
Immunohistochemistry of paraffin-embedded human breast cancer using CSB-PA05865A0Rb at dilution of 1:100
Overlay Peak curve showing HepG2 cells stained with CSB-MA015943A0m (red line) at 1:50.
Immunofluorescent analysis of HepG2 cells using CSB-PA011590LA01HU at dilution of 1:100.
Detection Range:
6.25 pg/mL-400 pg/mL
Detection Range:
15.6 pg/ml-1000 pg/ml
Detection Range:
7.8 pg/mL-500 pg/mL
Detection Range:
7.8 pg/mL-500 pg/mL
References
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