Μελέτη της αγγειογένεσης σε λεμφώματα
ABSTRACT Background: Angiogenesis denotes the formation of new blood vessels from preexisting ones. It is an adaptive mechanism of the human body and is controlled by a fine balance between pro- and anti-angiogenic factors. In solid tumours, the balance is lost in favour of proangiogenic signals promoting the growth and dissemination of the tumour. Hodgkin and Non Hodgkin lymphomas are lymphoid malignancies with unique biological and immunological features. The degree of dependence of lymphomas on angiogenesis is currently unknown. Aim: The aim of the current study was to examine the role of angiogenesis in Hodgkin and B cell Non Hodgkin lymphomas. In order to achieve this, the histological and peripheral expression of a series of active molecules and their receptors as well as the microvessel density was measured in affected lymphomas. The relation of angiogenesis to the peripheral expression of representative inflammatory and immunomodulatory cytokines was also determined. Materials & Methods: In the prospective part of this study, serum was collected from 60 newly diagnosed Hodgkin patients and used to determine the concentration of: VEGF (vascular endothelial growth factor), receptor VEGF R2, HGF (hepatocyte growth factor), bFGF (basic fibroblast growth factor), angiogenin, angiopoietin-2, MMP-2 (metalloproteinase-2), IL-8, TNFα, IL-6, IL-10 και IL-12 by the ELISA method. Serum was also collected from 49 newly diagnosed patients with Non Hodgkin Lymphoma for the measurement of VEGF, angiogenin, IL-8, IL-6, IL-2 and IL-16. The aforementioned molecules were determined in a subgroup of patients at the end of standard treatment and in a group of normal controls. In the retrospective part of this study, the histological expression of microvessel density (using an anti-CD31 antibody), VEGF, PDGFRα (platelet derived growth factor receptor α), HIF-1α (hypoxia inducible factor 1α), Ki-67 and p53 was assessed in 65 Hodgkin lymph nodes by immunohistochemistry. Results: In Hodgkin lymphomas there is increased peripheral expression of the angiogenic molecules HGF, VEGF and IL-8 in comparison to healthy controls, which decreases after effective treatment. Increased levels of HGF and IL-8 are associated with advanced stages of disease. Prognostic value is attributed to HGF as serum levels below 2306 pg/ml are associated with a higher probability of complete response to treatment. The inflammatory response comprises an increase in the levels of TNFα and IL-6. IL-6 levels show a positive association with HGF and VEGF levels. The immunological response is characterized by a predominance of IL-10 (indicative of a Th2 response) and depressed levels of IL-12. Immunohistochemical expression of VEGF and p53 in the reactive cells of Hodgkin lymphoma was found at the initial stages of the disease. Neoplastic cells show strong staining of PDGFRα in the majority of cases and weak staining of HIF-1α in half of the cases examined. Microvessel density is not increased in Hodgkin in comparison to normal lymph nodes but increases in parallel to the Ki-67 positivity of reactive cells. B Non Hodgkin lymphomas have increased peripheral levels of VEGF and IL-8, whereas angiogenin is within the normal range. The inflammatory response is characterized by an increase in IL-6, whereas the increase in IL-2 is indicative of a Th1-type immunological reaction. Conclusions: 1. Increased histological expression of key angiogenic factors is observed in Hodgkin tissues. 2. There is also an increase in the levels of angiogenic factors in the serum of Hodgkin and Non Hodgkin patients. 3. The release of angiogenic factors in the periphery relates to the release of inflammatory cytokines supporting a role of inflammation as a positive feedback in angiogenic signalling. 4. The difference in prevailing angiogenic signals between the two lymphomas may be associated with the specific immunological reaction. This is supported by the difference in cytokine profile seen between Hodgkin (dominant Th2) and Non Hodgkin (dominant Th1 reaction) lymphoma. 5. The microvessel density in Hodgkin lymph nodes is not increased in comparison to normal lymph nodes implying alternative roles (rather than vessel formation) for overexpressed angiogenic molecules. Such roles may be the positive control of lymphangiogenesis, inflammation and immunosuppression. 6. The relation of microvessel density to Ki-67 in reactive cells implies that increased blood supply is important mainly for the reactive dividing compartment rather than the malignant Hodgkin clone itself. 7. The dominant angiogenic pathways in Hodgkin lymphoma are HGF and PDGF, which may prove useful for the selection of specific anti angiogenic treatment in the future.