|Year : 2019 | Volume
| Issue : 3 | Page : 564-570
A correlation of immunohistochemical expression of TP53 and severity of inflammation with varying grades of oral squamous cell carcinoma
Jay Ashokkumar Pandya1, Srikant Natarajan2
1 Department of Oral Pathology, Ambika Dental Clinic and Oral Histopathology Laboratory, Bharuch, Gujarat, India
2 Department of Oral Pathology and Microbiology, Manipal College of Dental Sciences, Manipal University, Mangalore, Karnataka, India
|Date of Web Publication||29-May-2019|
Dr. Jay Ashokkumar Pandya
Ambika Dental Clinic and Oral Histopathology Laboratory, Attohid Park, Rahadpor, Bharuch, Gujarat
Source of Support: None, Conflict of Interest: None
Purpose: Epithelial cells exposed to carcinogens and genetic damage, once surpass reversible cell damage, either undergo apoptosis or transform into malignancy, chiefly oral squamous cell carcinoma (OSCC). Progressive accumulation of genetic errors in TP53 results in tumorigenesis. Inflammation is also a modulator in this process. The present study attempted to correlate the immunohistochemical expression of TP53 with increased aggressiveness of OSCC, to determine how these immune cells regulate the path of carcinogenesis and to define the role of inflammation in TP53 immunoexpression.
Materials and Methods: Tissue sections from 24 biopsy-proven cases of OSCC were stained with anti-TP53 antibody. Five hundred neoplastic epithelial cells and inflammatory cells, each, were counted at invasive tumor front. Two hundred peritumoral neutrophils were counted based on nuclear lobes present.
Results: The least TP53 expression was seen in well-differentiated OSCC (P < 0.001), whereas neutrophil count and plasma cell count were found to be least in well-differentiated OSCC (P < 0.001), whereas the number of lymphocytes and macrophages decreased with increased grading of OSCC (P < 0.001). Four- and five-lobed neutrophils were found to be highest in poorly differentiated OSCC (P < 0.001), whereas two-lobed neutrophil count was seen to be maximum in well-differentiated OSCC (P < 0.001).
Conclusion: TP53 plays a significant role in the initiation and progression of OSCC. Inflammation plays a role of friend and a foe simultaneously, and little modification in the present treatment modalities for OSCC can bring a favorable change in the life of cancer survivors.
Keywords: Inflammation, oral squamous cell carcinoma, TP53
|How to cite this article:|
Pandya JA, Natarajan S. A correlation of immunohistochemical expression of TP53 and severity of inflammation with varying grades of oral squamous cell carcinoma. J Can Res Ther 2019;15:564-70
|How to cite this URL:|
Pandya JA, Natarajan S. A correlation of immunohistochemical expression of TP53 and severity of inflammation with varying grades of oral squamous cell carcinoma. J Can Res Ther [serial online] 2019 [cited 2020 Sep 22];15:564-70. Available from: http://www.cancerjournal.net/text.asp?2019/15/3/564/244234
| > Introduction|| |
TP53, which has rightly been called as “guardian of the genome,” is located at the short arm of the chromosome 17. It plays a key role in conferring DNA stability by halting cell cycle at G1-S phase in the presence of DNA damage. While sublethal damage activates the DNA repair protein, irreparable DNA damage drives the cell toward apoptosis. The inactivation of TP53 gene has been suggested to play a key role in many human tumors, and alteration in TP53 is thought to be an early event in the multistep carcinogenesis of oral epithelium. Accumulation of these abnormal proteins seems to be associated with poorer differentiation and progression of potentially malignant state and later, malignancy.,
Upon exposure of epithelial cells to carcinogen, interplay of diverse genes and their protein products enables the cells to adapt, as reflected by an increase in cell proliferation with diminishment of cytosolic volume and associated organellar load. When stages of adaptation and reversible cell damage are surpassed, cells enter into the stage of irreversible cell damage, manifested as cell death or neoplastic transformation, principally squamous cell carcinoma., Squamous cell carcinoma of the oral cavity, though closely associated with lifestyle factors, is also known to develop in the absence of these risk factors, thus emphasizing the role of genetic alterations (like TP53) that result in damage to signaling pathways and altered regulation of the cell cycle.,
Immune system is a chief modulator, which regulates the initiation and progression of any tumor. The crosstalk between immune system and cancer maintains an equilibrium between them; however when this equilibrium gets disoriented, it can lead to worse outcomes, principally by production of new tumor cell variants and accumulation of mutational changes by chance or in response to immune-mediated inflammation. Hence, immune system acts as a double-edged sword, which can both inhibit the tumor growth and enhance it.
Molecular changes, including TP53 mutation, have been linked to oral carcinogenesis. Cells of immune system and role played by them in guiding the course of tumor have always been a subject of controversy. The present study attempted to correlate the immunohistochemical expression of TP53 with increased aggressiveness of oral squamous cell carcinoma (OSCC), to determine how these immune cells regulate the path of carcinogenesis and to define the role of inflammation in TP53 immunoexpression.
| > Materials and Methods|| |
The study included a total of 24 cases of varying grades of OSCC. Four-μm-thick sections of each case were mounted on poly-L-lysine-coated slides. The sections were then dewaxed with xylene and rehydrated in graded ethanol. Endogenous peroxidase activity was blocked by placing the slides in methanol with 30% hydrogen peroxide for 10 min. The sections were then heated for antigen retrieval in 1500 ml citrate buffer (pH 6.0) for 20 min. Sections were then rinsed in tris buffer solution (TBS) (pH 7.6) and nonspecific conjugation was prevented with the use of Power Block (Universal Blocking reagent, Biogenex, CA) for 20 min. Incubation of sections with primary antibody against TP53 (mouse monoclonal anti-TP53, clone DO-7, Biogenex, Dilution 1:100) was done for 1 h at room temperature. Sections were rinsed with TBS, following addition of superenhancer to the sections for 30 min. Detection of conjugated antibody was done using Polymer (Polymer-HRP, Biogenex, CA) for 30 min. After washing with TBS, chromogen (3,3'-diaminobenzidine chromogen solution, Biogenex, CA) was applied for 10 min after which counterstaining with Mayer's hematoxylin was done. One positive control of breast carcinoma was included in each batch of immunostained sections. For negative control, the primary antibody was not added to the specimen.
Five hundred neoplastic epithelial cells from the invasive tumor front in OSCC were counted. Cells showing nuclear staining of TP53 were considered to be positive, whereas cells without nuclear staining or with cytoplasmic staining were considered to be negative. The percentage of cells with positive immunostaining was tabulated in each case. OSCC cases were differentiated into well-differentiated squamous cell carcinoma, moderately differentiated squamous cell carcinoma, and poorly differentiated squamous cell carcinoma based on the parameters used by Bryne et al. Severity of inflammation was graded based on quantification measures mentioned in Bryne's grading system  and was categorized as mild, moderate, and severe.
Five hundred inflammatory cells (including neutrophils, lymphocytes, plasma cells, and macrophages) were counted at peritumoral area and were tabulated. Two hundred neutrophils in the peritumoral region were counted separately and were subcategorized based on the number of nuclear lobes present (2–5 lobed).
Counting of TP53 and inflammatory cells and subcategorization of neutrophils were done under oil immersion objective lens (i NEA, 100×/1.25).
Comparison of TP53 expression, proportion of each inflammatory cell and neutrophil distribution between the grades of OSCC, and association of TP53 expression with severity of inflammation were done using one-way ANOVA and post hoc Tukey's test. Chi-square test was employed to find association of intensity of inflammation and differentiation of OSCC. The power of the study was kept at 80% and the level of significance at 5%. A 2-sided P < 0.05 was considered statistically significant for all tests. All statistical analyses were performed using SPSS v. 20. (IBM SPSS, USA).
| > Results|| |
The least TP53 expression was seen in well-differentiated OSCC (mean = 138) followed by moderately differentiated (mean = 202.5) and poorly differentiated OSCC ([mean = 296.25] [Figure 1], [Figure 2], [Figure 3] and [Table 1], P < 0.001]). The neutrophil count and plasma cell count were found to be least in well-differentiated OSCC and maximum in poorly differentiated OSCC [P < 0.001 and 0.153, respectively, [Table 1], whereas the number of lymphocytes and macrophages decreased with increased grading of OSCC [P < 0.001 and < 0.001, respectively, [Table 1]. On subcategorization of neutrophils, 4-lobed and 5-lobed neutrophils were found to be highest in poorly differentiated OSCC, and count was seen to be decreased with better differentiation [P < 0.001 and < 0.001, respectively, [Table 1], whereas 2-lobed neutrophil count was seen to be maximum in well-differentiated OSCC [P < 0.001, [Table 1]. Three-lobed neutrophils were found to be maximum in moderately differentiated OSCC followed by well-differentiated OSCC and poorly differentiated OSCC [P = 0.023, [Table 1]. Difference in TP53 expression was statistically significant between well-differentiated and poorly differentiated OSCC [P < 0.001, [Table 2] and moderately differentiated and poorly differentiated OSCC [P = 0.007, [Table 2]. The difference in neutrophil proportion, lymphocyte proportion, and 4-lobed and 5-lobed neutrophil count was statistically significant between well-differentiated and poorly differentiated OSCC [P < 0.001, <0.001, <0.001, and < 0.001, respectively, [Table 2] and between moderately and poorly differentiated OSCC [P = 0.002, <0.001, <0.001, and < 0.001, respectively, [Table 2]. The statistical difference in macrophage proportion and 2-lobed neutrophil count between well-differentiated and moderately differentiated OSCC [P = 0.03 and 0.023, respectively, [Table 2], well-differentiated and poorly differentiated OSCC [P < 0.001 and < 0.001, respectively, [Table 2], and between moderately differentiated and poorly differentiated OSCC [P = 0.031 and P = 0.004, respectively, [Table 2] was significant. Statistically, the difference in 3-lobed neutrophil count was significant between moderately and poorly differentiated OSCC [P = 0.024, [Table 2]. On comparing TP53 expression with the severity of inflammation, it was found that higher the severity of inflammation, higher the TP53 count [P = 0.782, [Table 3]. Intensity of inflammation was found to be reduced along with poorer differentiation of OSCC [P = 0.126, [Table 4].
|Figure 1: Immunohistochemical expression of TP53 in well-differentiated oral squamous cell carcinoma (a) ×10, (b) ×40, (c) ×100|
Click here to view
|Figure 2: Immunohistochemical expression of TP53 in moderately differentiated oral squamous cell carcinoma (a) ×10, (b) ×40, (c) ×100|
Click here to view
|Figure 3: Immunohistochemical expression of TP53 in poorly differentiated oral squamous cell carcinoma (a) ×10, (b) ×40, (c) ×100|
Click here to view
|Table 1: Comparison of TP53 expression, inflammatory cell proportion, and neutrophil subpopulation (based on nuclear lobes) with grades of oral squamous cell carcinoma – one-way ANOVA test|
Click here to view
|Table 2: Comparison of TP53 expression, inflammatory cell proportion, and neutrophil subpopulation (based on nuclear lobes) with grades of oral squamous cell carcinoma – post hoc Tukey's test|
Click here to view
|Table 3: Association of TP53 expression and severity of inflammation – ANOVA test|
Click here to view
|Table 4: Association of severity of inflammation with differentiation of oral squamous cell carcinoma – Chi-square test|
Click here to view
| > Discussion|| |
Carcinogenesis is multifactorial. The two major classes of genes, the proto-oncogenes and the tumor suppressor genes, regulate the fate of the lesion., TP53 is a marker which belongs to the tumor suppressor class. In the present study, TP53 expression was seen in all the 24 cases. We noted increased expression of TP53 with poorer differentiation of OSCC, thus suggesting a progressive accumulation of mutational errors of TP53 protein.,
The increase in the TP53 expression could be due to the increased transactivation or decreased destruction of the protein in the cytoplasm. Ionizing radiation, chemical carcinogens, and mutagens can cause DNA damage, which may activate or modify TP53 gene. Normally, TP53 activates MDM2 by binding to it and causing nuclear transcription. Tumor suppressor protein called p14ARF (the human homolog of mouse p19ARF [Alternative Reading Frame]) can bind to the MDM2 protein and form a complex with MDM2/TP53, causing its retention in the nucleus. Moreover, nuclear localization signals enable the entry of TP53 into the nucleus, whereas nuclear export signals and exportins are required for transfer of TP53 from nucleus into the cytoplasm to cause ubiquitination and its destruction. Hence, mutated p14ARF, MDM2, or exportins may also result in accumulation of TP53 in the nucleus.
Despite remarkable progress in treatment modalities for OSCC over the last few decades, survival rate at 5 years still prevails beneath 50%. It is attributed to its heterogeneous behavior. Tumor development and survival is principally governed by the processes involved in the interplay of cancer cells, normal stromal cells, and host defense mechanisms. Inflammation has evolved as a major factor amending cancer development, progression, and inhibition, and hence now considered as one of the hallmarks of cancer., The importance of strengthened immunity against tumor was seen in the present study, where we found reduced inflammation with poorer differentiation of tumor. In case of impaired immunity, tumor cells can easily traverse the path toward poorer differentiation. However, imbalance in immune system does not necessarily correlate with the number of defense cells that are present, but can also result from failure in functional regulation or migration of population of cells to tumor site. On the other hand, we also found that with increased severity of inflammation, there is increase in TP53 count indicative of genetic damage because of increased inflammation. It is plausible that TP53 dysfunction may also contribute immunologically to tumorigenesis and tumor progression by altering host immune response. Studies have shown that TP53 inactivation plays a supporting role in inflammation-induced tumorigenesis. More importantly, TP53 inactivation-mediated elevation of inflammatory molecules is not restricted to immune cells, but its mutation in cancer-associated fibroblast augments the production of pro-inflammatory molecules. In case of severe inflammation, there are elevated levels of reactive oxygen species (ROS), which have a major role in cancer development. Increased ROS has been seen in cancer cells. With increased ROS, there is increased oxidative damage, resulting in subsequent double-stranded DNA breaks. Consequently, it results in the accumulation of repeated DNA insults, resulting in worsening of tumor.
In the present study, we counted 500 inflammatory cells in peritumoral infiltrate and quantified them as neutrophils, lymphocytes, plasma cells, and macrophages and compared their count with differentiation of OSCC. As neutrophils are in abundance, they participate in nearly every step of tumorigenesis. Hence, we counted 200 neutrophils separately and subcategorized them based on the number of lobes in their nuclei. In the present study, it was not possible to subcategorize lymphocytes and macrophages because bio-molecular methods were not employed.
In the present study, we found increased neutrophil count with poorer differentiation of OSCC. Although neutrophils are key mediators of innate immune system, required to protect the host system against infection and promote healing, studies have shown that it also contributes to tumor progression, metastasis, and extracellular trap-dependent tumor metastasis. Neutrophil-secreted products such as human defensins, tumor necrosis factor (TNF) proteins, and neutrophil gelatinase-associated lipocalin have been found to be elevated with poorer differentiation of OSCC. Defensins are known to induce cytotoxic effects in numerous target cells. Lundy et al. found 10–12 fold increase of defensins in localized tumor areas. Members of TNF family, APRIL, TNF-related apoptosis-inducing ligand (TRAIL), and DR5, have been found to be elevated in OSCC. APRIL regulates tumor cell survival and proliferation through binding to heparin sulfate and chains of proteoglycans or to calcium modulation and cyclophilin ligand interactor. Jablonska et al. found increased expression of APRIL in OSCC with poor prognosis and poorer differentiation. TRAIL induces apoptosis by activation of DRs including DR1 and DR5. Neutrophils also secrete matrix metalloproteinase (MMPs) 8 and 9, diastase, cathepsin, and proteinase-3. All these molecules play a significant role in remodeling of tumor microenvironment by directly degrading the extracellular matrix, and hence help the tumor to march toward poorer differentiation. Neutrophils also activate membrane Type I MMP in tumor cells and facilitate cancer progression indirectly. Neutrophil also upregulates secretion of vascular endothelial growth factor, resulting in angiogenesis., Few studies have shown that neutrophils secrete pro-MMP 9 without tissue inhibitor of metalloproteinase, providing readily active MMP 9-promoting tumor angiogenesis and metastasis. On subcategorization of neutrophil lobe wise, we found the highest number of 2-lobed neutrophils in well-differentiated OSCC and least in poorly differentiated OSCC. Bilobed nuclei is an indication of immaturity and suggests that bone marrow is releasing cells before nuclei are completely segmented, a common phenomenon during tumorigenesis. This indicates a hyperimmune response, limiting the worsening of the tumor, as reflected in our study. Four- and five-lobed nuclei were seen to be maximum in poorly differentiated carcinoma, decreasing with better differentiation. Four- and five-lobed neutrophils indicate senescent neutrophils, hence incapable of providing strengthened antitumor immunity. It could also be because of comorbidities such as anemia, more commonly seen with poorer differentiation of OSCC. Hence, poorer differentiation of OSCC, in relation to neutrophil count, is chiefly because of their increased proportion in peritumoral infiltrate and their dysfunction, due to senescence and comorbidities, consequence of it being a failure in providing a wall of defense against tumor cells.
Lymphocytes curb cancer development, mainly by production of interferon and cytotoxins. In the present study, they were found to be reduced with poorer differentiation of tumor cells. This could be because of decreased recruitment of lymphocytes due to production of several immunosuppressive cytokines, either by cancer cells or by noncancerous cells. Other reason could be ganglioside antigen, present on the cell surface, or which sheds from the cell surface, which is known to suppress lymphocyte. Furthermore, immunosuppressive enzymes such as arginase and indoleamine-pyrrole 2, 3-dioxygenase inhibit lymphocyte activity. Their secretion is found to be higher with poorer differentiation of tumor cells. These enzymes can also contribute to tumor progression through tumor cell proliferation. This also points toward tumor cells failing in expressing co-stimulatory molecules, resulting in induction of anergy or tolerance by engaging cell receptor. Studies have also shown that cancer cells can deplete lymphocytes by apoptosis. Affonso et al. in their study found that higher the count of lymphocytes in peritumoral infiltrate, better is the prognosis. Worsening of tumor can also result when cellular immunity deficits in interaction between monocyte chemotaxis and in interaction between monocytes that have antigen and lymphocytes.
Macrophages are an important component of innate immunity system associated with tissue remodeling, inflammation, and immunity. Depending on their activation, macrophages can secrete growth factors, prostaglandins, interferon, elastase, plasminogen activator, and collagenase and complement components. Classically activated macrophages are M1 macrophages and alternatively activated are M2 macrophages. Their differentiation is mediated through the release of cytokines and growth factors present in inflammatory microenvironment. It has been found in a number of tumor models that macrophages support cancer cells with proliferation and survival. However, in the present study, we found decrease in macrophage count with poorer differentiation. This again signifies the poor immunity associated with poorer differentiation of OSCC. Moreover, lymphocytes produce molecules that activate or alternatively activate macrophage, and these sense pathogen-associated molecular pattern and amplify M1 or M2 response. Hence, reduced macrophage with poorer differentiation could be related to reduced lymphocyte count observed in poorly differentiated OSCC.
The plasma cell distribution was found to be almost similar among all the three grades of OSCC; however, it was seen to be higher in poorly differentiated OSCC. Studies have shown that though immunity maintains an inhibitory effect on tumor, chronic inflammation may override these effects, leading to cancer development, growth, and angiogenesis, and hence poorer differentiation. This occurs chiefly because plasma cells enhance the production of inflammatory mediators, which triggers neoplastic transformation and worsening of already existing tumor.
| > Conclusion|| |
This study highlights the role of TP53 in the initiation and progression of OSCC. In addition, inflammation is a double-edged sword, with liabilities under the shadow of assistance. Although it provides defense against neoplasm, it can turn the same neoplasm into a lethal weapon against the same host if situation arises. Understanding how individual cells modify the course of a neoplasm may help to modify the molecular structure, mechanism, and dosage of immunomodulatory drugs. Furthermore, extensive studies are required to solve the mysterious role of inflammation in tumorigenesis so that a little modification in the present treatment modalities can bring a huge favorable change in the life of cancer survivors.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| > References|| |
Kaur J, Srivastava A, Ralhan R. Prognostic significance of p53 protein overexpression in betel- and tobacco-related oral oncogenesis. Int J Cancer 1998;79:370-5.
Heah KG, Hassan MI, Huat SC. P53 expression as a marker of microinvasion in oral squamous cell carcinoma. Asian Pac J Cancer Prev 2011;12:1017-22.
Tandle AT, Sanghvi V, Saranath D. Determination of p53 genotypes in oral cancer patients from India. Br J Cancer 2001;84:739-42.
Sharma N, Hosmani JV, Tiwari V. Epithelial dysplasia: Different grading system and its applications. J Int Oral Health 2010;2:1-16.
Rajendran R, Sivapathasundharam B. Benign and malignant tumours of the oral cavity. In: Shafer's Textbook of Oral Pathology. 7th
ed. India: Elsevier; 2012. p. 87-9.
Gomes CC, Drummond SN, Guimarães AL, Andrade CI, Mesquita RA, Gomez RS, et al.
P21/WAF1 and cyclin D1 variants and oral squamous cell carcinoma. J Oral Pathol Med 2008;37:151-6.
Todd R, Hinds PW, Munger K, Rustgi AK, Opitz OG, Suliman Y, et al.
Cell cycle dysregulation in oral cancer. Crit Rev Oral Biol Med 2002;13:51-61.
Vinay DS, Ryan EP, Pawelec G, Talib WH, Stagg J, Elkord E, et al.
Immune evasion in cancer: Mechanistic basis and therapeutic strategies. Semin Cancer Biol 2015;35 Suppl:S185-98.
Bryne M, Koppang HS, Lilleng R, Stene T, Bang G, Dabelsteen E, et al.
New malignancy grading is a better prognostic indicator than Broders' grading in oral squamous cell carcinomas. J Oral Pathol Med 1989;18:432-7.
Carlos de Vicente J, Junquera Gutiérrez LM, Zapatero AH, Fresno Forcelledo MF, Hernández-Vallejo G, López Arranz JS, et al.
Prognostic significance of p53 expression in oral squamous cell carcinoma without neck node metastases. Head Neck 2004;26:22-30.
Chandra P, Agnihotri PG, Nagarathna S. Expression of p53 protein in premalignancies and squamous cell carcinoma of the oral cavity. J Indian Acad Oral Med Radiol 2012;24:300-5. [Full text]
Regezi JA, Zarbo RJ, Regev E, Pisanty S, Silverman S, Gazit D, et al.
P53 protein expression in sequential biopsies of oral dysplasias and in situ
carcinomas. J Oral Pathol Med 1995;24:18-22.
Nylander K, Dabelsteen E, Hall PA. The p53 molecule and its prognostic role in squamous cell carcinomas of the head and neck. J Oral Pathol Med 2000;29:413-25.
Affonso VR, Montoro JR, Freitas LC, Saggioro FP, Souza LD, Mamede RC, et al.
Peritumoral infiltrate in the prognosis of epidermoid carcinoma of the oral cavity. Braz J Otorhinolaryngol 2015;81:416-21.
Zelenay S, van der Veen AG, Böttcher JP, Snelgrove KJ, Rogers N, Acton SE, et al.
Cyclooxygenase-dependent tumor growth through evasion of immunity. Cell 2015;162:1257-70.
Guo G, Cui Y. New perspective on targeting the tumor suppressor p53 pathway in the tumor microenvironment to enhance the efficacy of immunotherapy. J Immunother Cancer 2015;3:9.
Bjørn ME, Hasselbalch HC. The role of reactive oxygen species in myelofibrosis and related neoplasms. Mediators Inflamm 2015;2015:648090.
He G, Zhang H, Zhou J, Wang B, Chen Y, Kong Y, et al.
Peritumoural neutrophils negatively regulate adaptive immunity via the PD-L1/PD-1 signalling pathway in hepatocellular carcinoma. J Exp Clin Cancer Res 2015;34:141.
Shatz M, Shats I, Menendez D, Resnick MA. P53 amplifies toll-like receptor 5 response in human primary and cancer cells through interaction with multiple signal transduction pathways. Oncotarget 2015;6:16963-80.
Li Q, Verma IM. NF-kappaB regulation in the immune system. Nat Rev Immunol 2002;2:725-34.
Nikulenkov F, Spinnler C, Li H, Tonelli C, Shi Y, Turunen M, et al.
Insights into p53 transcriptional function via genome-wide chromatin occupancy and gene expression analysis. Cell Death Differ 2012;19:1992-2002.
Inuwa IM, Viernes N, Zaidan Z. A stereological study on azurophilic and specific granules in neutrophils of patients with schizophrenia before and during antipsychotic treatment. Eur J Gen Med 2004;1:15-21.
Khan MA, Assiri AM, Broering DC. Complement and macrophage crosstalk during process of angiogenesis in tumor progression. J Biomed Sci 2015;22:58.
Mills CD, Lenz LL, Ley K. Macrophages at the fork in the road to health or disease. Front Immunol 2015;6:59.
[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3], [Table 4]