Arvo building, auditorium F114, address: Lääkärinkatu 1
Faculty of Medicine and Life Sciences
The field of science of the dissertation is Pediatrics/Molecular Biology.
The opponent is Professor Markku Heikinheimo (University of Helsinki). Professor Kalle Kurppa acts as the custos.
The language of the defence is Finnish.
In coeliac disease, dietary gluten from wheat, barley and rye induces an autoimmune reaction in genetically susceptible individuals. This involves the formation of coeliac disease-specific antibodies targeting mainly transglutaminase 2 (TG2). TG2 autoantibodies are present both in the circulation and as deposits in the small-intestinal mucosa already in very early phases of the disease. Usually these autoantibodies belong to immunoglobulin (Ig) class A, but IgA deficient coeliac patients have IgG class antibodies in their circulation, and IgM antibodies have been found in the small-intestinal mucosa. Typically patients also evince small-bowel mucosal damage which develops gradually from normal villous morphology to inflammation and finally to crypt hyperplasia and villous atrophy. Furthermore, it has been shown that coeliac patients evince abnormalities in small-intestinal vasculature, which supplies an essential mechanical support for the villous structure. The clinical presentation of the disease is variable, ranging from asymptomatic to classical intestinal manifestations such as diarrhoea and abdominal pain, and even to extraintestinal symptoms in different organs involving for instance liver, skin, muscles and brain. Interestingly, many of these have been reported to occur while the small-intestinal morphology is still normal.
Many studies have shown that TG2 autoantibodies have biological effects in vitro, but there is controversy as to their contribution to the disease pathogenesis. The present work aimed to demonstrate in vivo effects of coeliac disease patient antibodies and especially TG2-targeted autoantibodies relevant to the pathogenesis of the disease. Studies I and II were conducted using a passive transfer method, where either sera or serum total IgG fraction from IgA deficient coeliac disease patients (I) or patient-derived recombinantly produced TG2 autoantibodes (II) were injected into mice lacking T cells. In study III, in vitro, ex vivo and in vivo matrigel assays were utilized to investigate the effects of TG2 autoantibodies on vascular formation and functionality.
In studies I and II, mice receiving coeliac patient-derived sera, total IgG or monoclonal TG2 autoantibodies evinced a slight, albeit significant, deterioration of the mucosal morphology in the small intestine. In addition, an increased density of infiltrative cells in the lamina propria was observed. Autoantibody deposits targeted to TG2 were also found in the small-intestinal mucosa of the mice. None of these features was observed in control mice. Interestingly, an increased occurrence of mild diarrhoea and delayed weight gain was observed in a subset of the mice injected with coeliac patient sera or total IgG in study I. In contrast, in study II, injections of TG2 autoantibodies led to no such difference in the occurrence of mild diarrhoea between groups and the weights of the mice were fairly stable throughout the study period.
The results from study III clearly showed that coeliac patient-derived antibodies inhibited angiogenesis in vitro, ex vivo and in vivo. In in vitro studies the cells were less mobile in the presence of coeliac antibodies compared to controls and ex vivo results further revealed that, in the presence of coeliac patient TG2-targeted autoantibodies, cells outgrowing from mouse aortas were round and did not exhibit cellular processes characteristic for the leading edge during migration as in controls. Thus it might be assumed that inhibited angiogenesis is accounted for defective cell migration. In addition, the in vivo study revealed impaired functionality of vessels in the presence of coeliac antibodies.
For the first time, TG2 targeted autoantibody deposits were shown in the small-intestinal mucosa of mice. Importantly, autoantibody deposits occur in conjunction with mild enteropathy in mice. The condition of mice receiving coeliac patient-derived sera, total IgG or TG2 autoantibodies resembled early-phase disease in coeliac patients.
Based on the data from the present study, it seems conceivable that an increased density of inflammatory cells in the lamina propria, together with the slightly increased levels of tumor necrosis factor (TNF)-α and interleukin (IL)-27 seen in study II, may contribute to small-intestinal mucosal deterioration and thus play a role in the pathogenesis of coeliac disease. In addition, study III revealed the anti-angiogenic effects of coeliac TG2 autoantibodies and thus it may be assumed that small-intestinal deposits may contribute to the development of villous atrophy by impairing the intestinal vascularity and leaving the villi without proper mechanical support. The results from the present study would also imply that the development of clinical features requires, in addition to the TG2 autoantibodies used in the present study, also TG2 autoantibodies targeting other epitopes in TG2, entirely other antibody populations and/or longer exposure to the antibodies. Altogether, this study provided new evidence on the biological effects of coeliac disease-specific autoantibodies in vivo.
The dissertation is published in the publication series of Acta Universitatis Tamperensis; 2243, Tampere University Press, Tampere 2016. ISBN 978-952-03-0303-7, ISSN 1455-1616. The dissertation is also published in the e-series Acta Electronica Universitatis Tamperensis; 1743, Tampere University Press 2016. ISBN 978-952-03-0304-4, ISSN 1456-954X.
Suvi Kalliokoski, email@example.com