14th EFLM Continuous Postgraduate Course in Clinical Chemistry and Laboratory Medicine Diabetes as autoimmune disease - manifested T1D is based traditionally on diabetes Diabetes type I mellitus typical clinical symptoms: polyuria, in- creased thirst, weight loss, weakness, hunger, re- current infection and in severe insulinopenia the Evgenija Homsak patient are prone to diabetic ketoacidosis . Impor- Department for Laboratory Diagnostics, University Clinical tant diagnostic parameters are also for T1D char- Centre Maribor, Maribor, Slovenia acteristic HLA gene and especially different auto- antibodies against antigens of β cells, which could Corresponding author: evgenija .homsak@ukc-mb .si be present several years before clinical manifesta- tion of disease . Introduction Type 1 diabetes mellitus (T1D), also known as insu- Pathogenesis lin - dependent diabetes mellitus, is a chronic im- T1D is an autoimmune disorder against the β cells mune mediated disease that is characterized by of the pancreatic islets, that remain only 10-20% selective loss of insulin producing β cells of the functioning at the time of diagnosis . For T1D is pancreatic islets in genetically susceptible sub- characteristic subclinical prodrome of variable du- jects . The majority (95%) of cases are attributable ration, as the pathogenetic process begins years to an autoimmune-mediated destruction of β cells before the clinical onset, when the tolerance to (type 1a) while a small minority (5%) of cases re- self-autoantigens is lost (5) . The whole process and sults from an idiopathic destruction or failure of β factors that contribute to and influence the de- cells (type 1b) (1) . T1D is observed in approximate- struction of the β cells is still not known . Still limit- ly 5-10% of diabetes mellitus patient . It may be ed current knowledge of pathogenesis of T1D as present at any age and with equal affection of autoimmune disease is based on several impor- both sexes . It appears most typically in early life tant known facts, which have been gained with a peak around the puberty, but one-fourth of through several studies, mostly using animal mod- cases are diagnosed in adults . T1D remains the els and confirmed by human clinical trials . This most common form of diabetes in childhood, ac- process occurs in genetically susceptible subjects, counting for approximately two-thirds of new di- is probably triggered by one or more environmen- agnoses of diabetes in patients ≤19 years of age in tal agents, and usually progresses over many the United States, despite the increasing rate of months or years during which the subject is type 2 diabetes . The incidence of T1D varies 50- asymptomatic and euglycemic . Important genetic 100 fold around the world, with the highest rates predisposition in the presence of not yet defined in northern Europe, with 57 4. cases/100 0. 00 per triggers and modulators from the environment year in Finland and with relatively low incidence of could influence on modulation of immune system 0 6. /100 0. 00 in China (2) . The incidence of child- to lose the tolerance to auto-antigens and results hood T1D is rising rapidly in all population, espe- with several autoimmune reactions, local inflam- cially in the age under 5 years, that suggests a mation (insulitis), specific T cell (LyT) and B cell strong environmental contribution . Lately, (LyB) responses, autoantibody production, and cell through several studies, there are strong efforts to destructions . The proposed mechanism of autoim- understand and explain pathogenesis and find mune inflammation process start with presenta- the new therapeutic options of the disease ac- tion of self antigens on antigen presenting cells cording to potential auto-antigens (insulin) and (dendritic, LyB, macrophage), that after releasing different environmental factors, as an important interleukin (IL)-12 activate LyT (CD4 T) that produce key in the development of T1D . But the role of spe- important key cytokine INF-γ . They inhibit Th2 cy- cific factors such as viruses or ingested food (milk) tokine production, enhance production of toxic remains controversial (3,4) . Diagnosis of clinical cytokine (IL-β, TNF-α) and free radical by mac- Biochemia Medica 2014;24(Suppl 1):S1-S78 S35 Supplement.indd 35 20.10.2014. 8:44:04 14th EFLM Continuous Postgraduate Course in Clinical Chemistry and Laboratory Medicine rophage, and activate cytotoxic CD8T cells that af- ulation is important for predicting disease, accura- fects the β cells . Important connection between cy of diagnosis, prognosis and treatment . LyT and LyB causes activation of LyB for produc- LyT and LyB involvement: Autoimmunity and in- tion of auto-antibodies . Auto-antibodies, several volvement of LyT is further supported with the cytokines, cytotoxic CD8T cells with releasing per- presence of specific LyT infiltrates within inflamed forine, granzymes or by Fas-mediated apoptosis islets of pancreas of patient with T1D, according to affect and progressively destroy the β cells . Addi- Imagawa and co-workers, who found close corre- tionally local chemokine production attracts auto- lation between serological and histological mark- reactive lymphocytes that potentiate the destruc- ers and histological evidence of cellular autoim- tive autoimmune process . (4,5,6) In pathogenesis munity (10) . Insulitis as autoimmune inflammation of T1D we could find some similarities with other could be present years before hyperglycemia is autoimmune diseases, like celiac disease; the com- evident . Ly B cells also serve as antigen presenting mon genetic susceptibility, unknown hypothetical cells and as autoantibodies producing cells (6) . trigger from environment, infection, driving auto- Both Ly as important actors of disease could be antigen, autoantibodies and outcome (1/5 of with target of the future therapeutic options . HLA conferred susceptibility progresses to clinical disease) . Autoantibodies: There are five disease related autoantibodies: islet cell antibodies (ICA), insulin Genetics: Disease susceptibility is highly associat- autoantibodies (IAA) with epitope on B-chain of ed with the inheritance or presence of certain hu- insulin molecule, autoantibodies against 65-kDa man leukocyte antigen (HLA), which is characteris- isoform of glutamic acid decarboxilase (GAD65), tic for autoimmune diseases . HLA molecules are tyrosine phosphatase related IA-2 molecule or in- responsible for presentation of peptides (also au- sulinoma associate antigen-2 antibodies (IA-2) and to-antigens) to Ly T cells and are involved in thym- zinc transporter protein (ZnT8) . Presence of auto- ic selection of new generated T cell repertoire antibodies are evident years before clinical onset (central tolerance), to avoid potential autoimmune and are mostly the first sign of autoimmune pro- clones that could be released into the periphery . cess, that will or not progress to T1D . Several stud- Therefore, a defect within the thymus or presence ies confirm their important role in prediction of of specific HLA molecules allows autoimmune T the disease development and appearance accord- cells to escape central tolerance . HLA genes on ing to the detection of different specific autoanti- short arm of chromosome 6p21 3. with alleles DR3 bodies (4,5,11) . Mrena and co-workers in the Finn- and DR4 as well as the associated alleles DQ2 and ish DIPP study observed that presence of positivity DQ8, that are expressed either as DR3DQ2 or for only a single autoantibody specificity for sev- DR4DQ8, are present in more than 90% of individ- uals with T1D (7) . Remain 10% of T1D might have eral years represents in most cases harmless non- influence of 20 non-HLA genes . Among them are progresive β cell autoimmunity, whereas the pres- important polymorphisms on insulin locus on ence of two or more autoantibodies reflects a pro- chromosome 11p5,5 (PTPN22 and INS VNTR) that gressive process (10) . But their direct pathogenetic contributes approximately 10% to the familial ag- role is controversial, since transfer of autoantibod- gregation of disease (8) . As with HLA, peripheral T ies, using serum of diabetic humans, alone did not cell repertoires may be significantly influenced by reconstitute disease and that plasmapheresis pro- polymorphisms in the insulin gene affecting thy- vides little therapeutic benefit (6,12) . mocyte selection . Recent studies identifies auto- Environment factors as a triggers and drivers immune disease associated polymorphisms of T of disease: There is still unexplained cause of ini- cell regulatory gene CTLA-4 (chromosome 2q22), tiation of the autoimmune process and why the that reduce the efficiency of regulatory function of auto-antigens become auto-antigenic . The factors LyT4CD4 cells (9) . Understanding the genetics of that control progression from insulitis (inflamma- T1D as well the determination of susceptible pop- tion of the β cells) to diabetes remain largely un- Biochemia Medica 2014;24(Suppl 1):S1-S78 S36 Supplement.indd 36 20.10.2014. 8:44:04 14th EFLM Continuous Postgraduate Course in Clinical Chemistry and Laboratory Medicine known . Understanding this may provide new op- Thus, genetic markers for T1D are present from portunities for preventing disease among popula- birth, immune markers are detectable after the tion with high risk for developing T1D or halt pro- onset of the autoimmune process, and metabolic gression of the β cells lost . markers can be detected with sensitive tests once There are recently several approaches for pre- enough β cell