Ko-stimuloivien T solureseptoreiden genetiikkaa CD28, CTLA4, ICOS ja PDCD1 immuniteetissa ja elinsiirroissa

Co-stimulatory signals are essential for the activation of naïve T cells and productive immune response. Naïve T cells receive first, antigen-specific signal through T cell receptor. Co-stimulatory receptors provide the second signal which can be either activating or inhibitory. The balance between signals determines the outcome of an immune response. CD28 is crucial for T cell activation; whereas cytotoxic T lymphocyte associated antigen 4 (CTLA4) mediates critical inhibitory signal. Inducible co-stimulator (ICOS) augments cytokine expression and plays role in immunoglobulin class switching. Programmed cell death 1 (PDCD1) acts as negative regulator of T cell proliferation and cytokine responses. The co-stimulatory receptor pathways are potentially involved in self-tolerance and thus, they provide a promising therapeutic strategy for autoimmune diseases and transplantation. The genes encoding CD28, CTLA4 and ICOS are located adjacently in the chromosome region 2q33. The PDCD1 gene maps further, to the region 2q37. CTLA4 and PDCD1 are associated with the risk of a few autoimmune diseases. There is strong linkage disequilibrium (LD) on the 2q33 region; the whole gene of CD28 exists in its own LD block but CTLA4 and the 5' part of ICOS are within a same LD block. The 3' part of ICOS and PDCD1 are in their own separate LD blocks. Extended haplotypes covering the 2q33 region can be identified. This study focuses on immune related conditions like coeliac disease (CD) which is a chronic inflammatory disease with autoimmune features. Immunoglobulin A deficiency (IgAD) belongs to the group of primary antibody deficiencies characterised by reduced levels of immunoglobulins. IgAD co-occurs often with coeliac disease. Renal transplantation is needed in the end stage kidney diseases. Transplantation causes strong immune response which is tried to suppress with drugs. All these conditions are multifactorial with complex genetic background and multiple environmental factors affecting the outcome. We have screened ICOS for polymorphisms by sequencing the exon regions. We detected 11 new variants and determined their frequencies in Finnish population. We have measured linkage disequilibrium on the 2q33 region in Finnish as well as other European populations and observed conserved haplotypes. We analysed genetic association and linkage of the co-stimulatory receptor gene region aiming to study if it is a common risk locus for immune diseases. The 2q33 region was replicated to be linked to coeliac disease in Finnish population and CTLA4-ICOS haplotypes were found to be associated with CD and IgAD being the first non-HLA risk locus common for CD and immunodeficiencies. We also showed association between ICOS and the outcome of kidney transplantation. Our results suggest new evidence for CTLA4-ICOS gene region to be involved in susceptibility of coeliac disease. The earlier published contradictory association results can be explained by involvement of both CTLA4 and ICOS in disease susceptibility. The pattern of variants acting together rather than a single polymorphism may confer the disease risk. These genes may predispose also to immunodeficiencies as well as decreased graft survival and delayed graft function. Consequently, the present study indicates that like the well established HLA locus, the co-stimulatory receptor genes predispose to variety of immune disorders.Ko-stimuloivien reseptoreiden välittämät signaalit ovat välttämättömiä naiivien T-solujen aktivoimiseksi. T-soluilla on tärkeä tehtävä immuunijärjestelmässä elimistön puolustautuessa taudinaiheuttajia vastaan. Oleellista on, että T-solut tunnistavat omat solut vieraista. Elinsiirtojen yhteydessä tarvitaankin voimakas lääkitys heikentämään immuunivastetta, joka kohdistuu elimistölle vieraita, siirrettyjä soluja vastaan. Pääsääntöisesti T-solut eivät reagoi omiin soluihin, mutta verenkiertoon pääsee joskus T-soluja, jotka hyökkäävät omaa elimistöä vastaan ja puhkeaa autoimmuunitauti kuten keliakia. Naiivit, eli antigeeniä aiemmin kohtaamattomat, T-solut tarvitsevat kaksi signaalia aktivoituakseen tehokkaiksi toimijoiksi. Ensimmäinen signaali on antigeenispesifinen ja välittyy varsinaisen T-solureseptorin kautta. Toinen, epäspesifinen signaali välittyy ko-stimuloivien reseptorien kautta. Ko-stimuloivia reseptoreita ovat mm CD28, CTLA4, ICOS ja PDCD1. Näitä reseptoreita koodittavat geenit kuuluvat samaan geeniperheeseen; ne ovat keskenään samankaltaisia ja ne sijaitsevat lähekkäin kromosomissa 2. Geeneissä on polymorfisia kohtia, joten eri yksilöillä esiintyy hieman eri muotoja samasta geenistä. Nämä periytyvät muutokset geeneissä voivat esimerkiksi altistaa yksilön keskimääräistä suuremmalle riskille sairastua autoimmuunitautiin tai siirretyn elimen hylkimiselle. Geenien eri muodot vaikuttavat siihen, miten paljon geenien koodittamia reseptoreita tuotetaan. Reseptorien muoto ja määrä puolestaan saattavat vaikuttaa siihen miten T-soluja aktivoidaan. Väitöskirjassa tutkittiin ko-stimuloivien T-solureseptoreiden geenien polymorfioita ja niiden yhteyttä keliakiaan, IgA-vasta-aineen puutokseen ja munuaissiirteen hylkimiseen. Tässä työssä etsittiin ICOS-geenistä ennen tuntemattomia polymorfisia kohtia ja määritettiin niiden yleisyys suomalaisilla. CTLA4 ja ICOS -geenien todettiin olevan hyvin läheisesti kytkeytyneet toisiinsa. Väitöskirjassa havaittiin CTLA4-ICOS-geenialueen tiettyjen polymorfoiden altistavan osaltaan keliakian puhkeamiselle. Lisäksi ICOS geenin tietyt muodot nostavat riskiä munuaissiirteen hitaalle käynnistymiselle. ICOS toimii myös immunoglobuliinien (Ig) luokanvaihdossa ja siten mahdollisesti IgA vasta-aineen puutoksen kehittymisessä. IgA-puutos ja keliakia esiintyvät usein samalla yksilöllä tai samassa perheessä. Tässä työssä havaittiin yhteinen perinnöllinen riskitekijä keliakialle ja IgA-puutokselle CTLA4-ICOS-geenialueella. Keliakian ja IgA puutoksen puhkeamiseen sekä munuaissiirteen toimivuuteen vaikuttavat useat eri geenit sekä lisäksi monet ympäristötekijät. Siten niiden ilmenemiseen vaikuttavien perinnöllisten tekijöiden tutkiminen on vaikeaa ja tulokset ovat usein tulkinnanvaraisia. CTLA4-geeniä on tutkittu paljon eri autoimmuunitauteihin liittyen. Aiemmin julkaistut ristiriitaiset tulokset voisivat selittyä sillä, että usea CTLA4-ICOS geenialueen polymorfia yhdessä (yksittäisen sijaan) lisää sairastumisriskiä

Secretion of celiac disease autoantibodies after in vitro gliadin challenge is dependent on small-bowel mucosal transglutaminase 2-specific IgA deposits

Background: In celiac disease gluten, the disease-inducing toxic component in wheat, induces the secretion of autoantibodies which are targeted against transglutaminase 2 (TG2). These autoantibodies are produced in the small-intestinal mucosa, where they can be found deposited extracellularly below the epithelial basement membrane and around mucosal blood vessels. In addition, during gluten consumption these autoantibodies can also be detected in patients' serum but disappear from the circulation on a gluten-free diet. Interestingly, after adoption of a gluten-free diet the serum autoantibodies disappear from the circulation more rapidly than the small-intestinal mucosal autoantibody deposits. The toxicity of gluten and the secretion of the disease-specific autoantibodies have been widely studied in organ culture of small-intestinal biopsy samples, but results hitherto have been contradictory. Since the mucosal autoantibodies disappear slowly after a gluten-free diet, our aim was to establish whether autoantibody secretion to organ culture supernatants in treated celiac disease patient biopsies is related to the duration of the diet and further to the preexistence of mucosal TG2-specific IgA deposits in the cultured biopsy samples. Results: In the organ culture system conducted with biopsies derived from treated celiac disease patients, gliadin induced secretion of autoantibodies to culture supernatants, reduced epithelial cell height and increased the density of lamina proprial CD25+ cells. However, these changes could be demonstrated only in biopsies from short-term treated celiac disease patients, where the small-intestinal mucosal TG2-specific IgA autoantibody deposits were still present. Furthermore, in these biopsies autoantibody secretion could be stimulated fully only after a 48-hour gliadin challenge. Conclusion: Our results show that studies focusing on the toxic effects of gliadin in the organ culture system should be carried out with biopsy samples from short-term treated celiac disease patients who are likely still to have mucosal IgA deposits present. In addition to providing an explanation for the discrepancies in previous publications, the present study also enables further validation of the organ culture method

Immunogenetic characteristics of patients with autoimmune gastritis

Peer reviewe

Endomysial antibodies predict celiac disease irrespective of the titers or clinical presentation

Peer reviewe

High-Density SNP Mapping of the HLA Region Identifies Multiple Independent Susceptibility Loci Associated with Selective IgA Deficiency

Selective IgA deficiency (IgAD; serum IgA<0.07 g/l) is the most common form of human primary immune deficiency, affecting approximately 1∶600 individuals in populations of Northern European ancestry. The polygenic nature of IgAD is underscored by the recent identification of several new risk genes in a genome-wide association study. Among the characterized susceptibility loci, the association with specific HLA haplotypes represents the major genetic risk factor for IgAD. Despite the robust association, the nature and location of the causal variants in the HLA region remains unknown. To better characterize the association signal in this region, we performed a high-density SNP mapping of the HLA locus and imputed the genotypes of common HLA-B, -DRB1, and -DQB1 alleles in a combined sample of 772 IgAD patients and 1,976 matched controls from 3 independent European populations. We confirmed the complex nature of the association with the HLA locus, which is the result of multiple effects spanning the entire HLA region. The primary association signal mapped to the HLA-DQB1*02 allele in the HLA Class II region (combined P = 7.69×10−57; OR = 2.80) resulting from the combined independent effects of the HLA-B*0801-DRB1*0301-DQB1*02 and -DRB1*0701-DQB1*02 haplotypes, while additional secondary signals were associated with the DRB1*0102 (combined P = 5.86×10−17; OR = 4.28) and the DRB1*1501 (combined P = 2.24×10−35; OR = 0.13) alleles. Despite the strong population-specific frequencies of HLA alleles, we found a remarkable conservation of these effects regardless of the ethnic background, which supports the use of large multi-ethnic populations to characterize shared genetic association signals in the HLA region. We also provide evidence for the location of association signals within the specific extended haplotypes, which will guide future sequencing studies aimed at characterizing the precise functional variants contributing to disease pathogenesis