Raivo Uibo

The geoepidemiology of type 1 diabetes.

Type 1 diabetes (T1D) is a chronic autoimmune disease characterized by absolute insulin deficiency resulting from the progressive immune-mediated destruction of pancreatic islet beta cells. It is thought to be triggered by as yet unidentified environmental factors in genetically susceptible individuals, the major genetic contribution coming from loci within the HLA complex, in particular HLA class II. The worldwide incidence of T1D varies by at least 100-fold, being highest in Finland and Sardinia (Italy) and lowest in Venezuela and China. The incidence has been increasing worldwide at an annual rate of approximately 3%. While genetic factors are thought to explain some of the geographic variability in T1D occurrence, they cannot account for its rapidly increasing frequency. Instead, the declining proportion of newly diagnosed children with high-risk genotypes suggests that environmental pressures are now able to trigger T1D in genotypes that previously would not have developed the disease during childhood. Although comparisons between countries and regions with low and high-incidence rates have suggested that higher socioeconomic status and degree of urbanization are among the environmental factors that play a role in the rising incidence of T1D, the findings are too inconsistent to allow firm conclusions. Morbidity and mortality as well as causes of death also show considerable geographic variation. While glycemic control has been identified as a major predictor of the micro- and macrovascular complications of T1D and shows considerable geographical variability, it does not appear to be the only factor involved in the regional differences in complication rates. The role of genetics in susceptibility to nephropathy, retinopathy and other diabetic complications largely remains to be explored.

Relationship between the incidence of type 1 diabetes and maternal enterovirus antibodies: time trends and geographical variation

Aims/hypothesisWe have previously observed an inverse correlation between the incidence of type 1 diabetes and enterovirus infections in the background population. The aim of this study was to analyse whether maternal enterovirus antibody status, which reflects both the frequency of enterovirus infections and the protection conferred by the mother on the offspring, also correlates with the incidence of type 1 diabetes.MethodsMaternal enterovirus antibodies were analysed from serum samples taken from pregnant women between 1983 and 2001 in Finland and Sweden using enzyme immunoassay and neutralisation assays. Comparable samples were also taken between 1999 and 2001 in countries with a lower incidence of diabetes (Estonia, Germany, Hungary, Israel, Lithuania, Russia).ResultsA clear decrease was observed in maternal enterovirus antibody levels over the past 20 years (p<0.0001). The frequency of enterovirus antibodies was higher in countries with a low or intermediate incidence of type 1 diabetes compared with high-incidence countries (p<0.0001).Conclusions/interpretationThese findings are in line with our previous observations supporting the hypothesis that a low frequency of enterovirus infection in the background population increases the susceptibility of young children to the diabetogenic effect of enteroviruses.

Aire-deficient C57BL/6 mice mimicking the common human 13-base pair deletion mutation present with only a mild autoimmune phenotype

Autoimmune regulator (AIRE) is an important transcription regulator that mediates a role in central tolerance via promoting the “promiscuous” expression of tissue-specific Ags in the thymus. Although several mouse models of Aire deficiency have been described, none has analyzed the phenotype induced by a mutation that emulates the common 13-bp deletion in human APECED (autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy) by disrupting the first plant homeodomain in exon 8. Aire-deficient mice with a corresponding mutation showed some disturbance of the medullary epithelial compartment, but at the phenotypic level their T cell compartment appeared relatively normal in the thymus and periphery. An increase in the number of activated T cells was evident, and autoantibodies against several organs were detected. At the histological level, lymphocytic infiltration of several organs indicated the development of autoimmunity, although symptoms were mild and the quality of life for Aire-deficient mice appeared equivalent to wild-type littermates, with the exception of male infertility. Vβ and CDR3 length analysis suggested that each Aire-deficient mouse developed its own polyclonal autoimmune repertoire. Finally, given the prevalence of candidiasis in APECED patients, we examined the control of infection with Candida albicans in Aire-deficient mice. No increase in disease susceptibility was found for either oral or systemic infection. These observations support the view that additional genetic and/or environmental factors contribute substantially to the overt nature of autoimmunity associated with Aire mutations, even for mutations identical to those found in humans with APECED.

Allergic sensitization and microbial load - a comparison between Finland and Russian Karelia

Epidemiological data have indicated that some infections are associated with a low risk of allergic diseases, thus supporting the idea (hygiene hypothesis) that the microbial load is an important environmental factor conferring protection against the development of allergies. We set out to test the hygiene hypothesis in a unique epidemiological setting in two socio‐economically and culturally markedly different, although genetically related, populations living in geographically adjacent areas. The study cohorts included 266 schoolchildren from the Karelian Republic in Russia and 266 schoolchildren from Finland. The levels of total IgE and allergen‐specific IgE for birch, cat and egg albumen were measured. Microbial antibodies were analysed against enteroviruses (coxsackievirus B4), hepatitis A virus, Helicobacter pylori and Toxoplasma gondii. Although total IgE level was higher in Russian Karelian children compared to their Finnish peers, the prevalence of allergen‐specific IgE was lower among Russian Karelian children. The prevalence of microbial antibodies was, in turn, significantly more frequent in the Karelian children, reflecting the conspicuous difference in socio‐economic background factors. Microbial infections were associated with lower risk of allergic sensitization in Russian Karelian children, enterovirus showing the strongest protective effect in a multivariate model. The present findings support the idea that exposure to certain infections, particularly in childhood, may protect from the development of atopy. Enterovirus infections represent a new candidate to the list of markers of such a protective environment. However, possible causal relationship needs to be confirmed in further studies.

Serum IgA anti-gliadin antibodies in an adult population sample. High prevalence without celiac disease.

IgA-class anti-gliadin antibodies (AGA) and IgA-, IgG-, IgM-class anti-reticulin antibodies (ARA) were determined in 1461 persons, representing 84% of a population from the village of Karksi-Nuia. AGA were detected by enzyme-linked immunosorbent assay (ELISA) and ARA by indirect immunofluorescence. Fifty-two (3.5%) persons had IgA-class AGA, of whom 48 and an additional three of four persons with diarrhea were biopsied. All biopsies showed normal small intestinal mucosal architecture. All 1461 persons were negative for ARA. Our results demonstrate that AGA are frequently detected in an adult Estonian population and positivity increases with age in persons with normal small intestinal mucosa. Positivity for AGA does not predict silent undetected celiac disease but rather represents a normal response to dietary antigens in the elderly. Inability to detect ARA suggests that celiac disease does not exist in this population. As none of the AGA-positive but ARA-negative biopsied persons had celiac disease, ARA might be a more specific serologic marker for celiac disease than AGA.

An 18-Year Follow-up Study of Chronic Gastritis and Helicobacter pylori: Association of CagA Positivity with Development of Atrophy and Activity of Gastritis

BACKGROUND We wanted to evaluate the course of chronic gastritis and its association with Helicobacter pylori and CagA seropositivity in an adult sample from Saaremaa (Estonia) during an 18-year follow-up. METHODS Seventy persons (31 men, 39 women; median age, 57.5 years) from a primary sample of 304 subjects endoscoped in 1979 were reinvestigated by endoscopy and biopsy in 1997. The state of the gastric mucosa and the presence of H. pylori in histologic sections from the antrum and corpus were assessed both in 1979 and 1997 in 66 subjects in accordance with the Sydney system, and H. pylori status in all 70 subjects was determined with the enzyme-linked immunosorbent assay (ELISA). Anti-CagA IgGs were determined with the ELISA, using the recombinant fragment of CagA. RESULTS During an 18-year follow-up 11% of the subjects developed atrophy in the antrum, whereas 35% developed it in the corpus. Development of atrophy in the corpus and the appearance of intestinal metaplasia in the antrum were associated with increased activity of gastritis both in the initial and last follow-up biopsies. Anti-CagA positivity was found in 71% of H. pylori-seropositive persons (94% of subjects). There was a significant association between CagA positivity and the activity of gastritis, the presence of atrophy or damage to surface epithelial cells in the antrum and in corpus mucosal biopsy specimens at the last follow-up endoscopy. CONCLUSION The CagA-positive strains of H. pylori enhance the development of atrophic gastritis compared with CagA-negative strains.

Primary Biliary Cirrhosis in Estonia with Special Reference to Incidence, Prevalence, Clinical Features, and Outcome

BACKGROUND Primary biliary cirrhosis (PBC) is a liver disease of unknown etiology, whose occurrence varies greatly between different regions. For a long time there have been no published data about the incidence and prevalence of PBC from Eastern Europe countries. METHODS The incidence and prevalence of PBC have been investigated in the Estonian population during the period 1973-92. Two sources of information were used: an information circular/questionnaire was sent to all district hospitals and gastroenterologists, and the case histories of all patients with a positive antimitochondrial antibody titer of 1:40 or more were reexamined. RESULTS During this period 69 cases of PBC were diagnosed. The male to female ratio was 1:22; 13% of the patients were asymptomatic. The mean annual incidence was 2.27 per million, and on 31 December 1992 the point prevalence was 26.9 per million. There were differences in prevalence among the various districts of Estonia. Associated autoimmune conditions were reported in 32% of the patients. Mean survival from the time of diagnosis was 52.5 months. CONCLUSIONS The incidence of PBC in Estonia is at the lower end of the range reported in the world literature. This has probably partly been caused by a low percentage of asymptomatic and male patients.

AIRE-Deficient Patients Harbor Unique High-Affinity Disease-Ameliorating Autoantibodies

Summary APS1/APECED patients are defined by defects in the autoimmune regulator (AIRE) that mediates central T cell tolerance to many self-antigens. AIRE deficiency also affects B cell tolerance, but this is incompletely understood. Here we show that most APS1/APECED patients displayed B cell autoreactivity toward unique sets of approximately 100 self-proteins. Thereby, autoantibodies from 81 patients collectively detected many thousands of human proteins. The loss of B cell tolerance seemingly occurred during antibody affinity maturation, an obligatorily T cell-dependent step. Consistent with this, many APS1/APECED patients harbored extremely high-affinity, neutralizing autoantibodies, particularly against specific cytokines. Such antibodies were biologically active in vitro and in vivo, and those neutralizing type I interferons (IFNs) showed a striking inverse correlation with type I diabetes, not shown by other anti-cytokine antibodies. Thus, naturally occurring human autoantibodies may actively limit disease and be of therapeutic utility.

High frequency of antigliadin antibodies and absence of antireticulin and antiendomysium antibodies in patients with ulcerative colitis.

Abstract: Several authors have described an association between celiac disease (CD) and ulcerative colitis (UC), but this has not yet been established. The aim of our study was to examine the frequency of antigliadin antibodies (AGA), antireticulin antibodies (ARA) and antiendomysium (AEM) antibodies in the sera of patients with UC (n = 50), and to evaluate their correlation with clinical variables. Sixteen patients with irritable bowel syndrome (IBS) and 37 healthy individuals served as controls. An enzyme-linked immunosorbent assay was used for the detection of IgA- and IgG-type AGA. IgG-type ARA were determined by an indirect immunofluorescence assay (IIF) using rat kidney, liver, and stomach as antigen substrates. IgA-type AEM antibodies were measured by IIF, using cryostat sections from human umbilical cord. Seventeen of the 50 patients with UC (34%) were positive for IgA- or/and IgG-type AGA. There was no correlation between the presence of AGA and the duration or extent of the disease, or disease activity. However, 5 patients with both IgA- and IgG-types of AGA had extensive colitis. Only 2 controls (4%) were positive for IgG-AGA. ARA and AEM were not detected in any individuals studied. Since the ARA and AEM test results were negative, we conclude that none of the UC patients in this series had CD.

The follow-up of asymptomatic persons with antibodies to pyruvate dehydrogenase in adult population samples

Purpose. The presence of antimitochondrial antibodies (AMA), the hallmark of primary biliary cirrhosis (PBC), precedes the clinical manifestation of the disease for many years. The main mitochondrial autoantigen is the E2 component of the pyruvate dehydrogenase complex (PDC). The aim of this study was to identify anti-PDC-positive persons from two Estonian populations by different methodologies and to follow up the positive cases. Methods. Enzyme-linked immunosorbent assay (ELISA) tests for antibodies to native PDC and recombinant PDC-E2 fusion protein were performed in 1461 persons (age range, 15–95 years) from Karksi-Nuia (plus 104 volunteers from the neighborhood) and to native PDC in 497 persons (age range, 50–91 years) from Abja-Paluoja (plus 28 volunteers from that neighborhood). Positive cases were tested with an enzyme inhibition assay. Results. We identified 14 asymptomatic persons with antibodies to native PDC and/or recombinant PDC-E2 from these two population samples. Eight of the 14 were available for follow-up. Three of the 8 developed abnormal liver biochemical test results by the ninth year of follow-up. These persons also had, or developed, during the follow-up, a positive AMA immunofluorescence test, inhibitory antibodies to PDC, and anti-PDC of at least IgG and IgA class. Five of the 8 persons with low levels of anti-PDC, of only one immunoglobulin class reacting with only one PDC preparation, did not show any signs of cholestasis or changes in their immunoreactivity during follow-up. Conclusions. A significant number of asymptomatic patients found to have antibodies to PDC are at high risk of developing primary biliary cirrhosis.