02 октября 2016г.
In the pathogenesis of systemic lupus erythematosus (SLE) an important place is given to immune mechanisms, many aspects of which remain unclear, in spite of the intensive study [6]. In recent years the attention is paid to the study of the relationship of autoimmune reactions and functioning of enzymes of major metabolic pathways of the organism, including purine metabolism (PM). Taking in account the characteristic immunological abnormalities in SLE it is reasonable to believe that a change in the enzymatic activity of some enzymes of the PM, such as xanthine oxidase (XO), adenosine deaminase (ADA) and adenosine kinase (ADK), may be connected not only to the effect of oxidation and metabolic disorders but also to the overproduction of autoantibodies to those enzymes.
The study of antibodies to XO (anti-XO) and identify of their effect on the activity of this enzyme in patients with SLE is of undoubted interest both from the point of diagnosis of pathological process activity and individual study of the pathogenesis of this disease [1, 3]. Previously, the participation of antibodies to the ADA (anti-ADA) in the development and maintenance of antiphospholipid syndrome (APS) by the impact of a possible conformational anti-ADA on b2-glycoprotein-I (b2 -GP-I), which may contribute to the expression of "hidden" epitopes in the molecule b2 -GP-I and as a consequence, to induce the synthesis of antibodies phospholipids [2, 7] was suggested.
The aim of our work was to study the processes of formation of autoantibodies to enzymes of purine metabolism - xanthine oxidase (XO, EC 1.1.3.22), adenosine deaminase (ADA, EC 3.5.4.4) and adenosine kinase (ADK, EC 2.7.1.20) - in SLE and identifying linkages of studied antibodies with clinical and laboratory features of the disease process.
Materials and methods.
30 healthy subjects 60 SLE patients [8] (women - 91.7%; the average age of 36,32 ± 15,27 years, the average duration of the disease 7,96±7,35 years) with different clinical manifestations (SLEDAI activity 8,93±5,74; ECLAM 5,30±2,79 activity, index SLICC / ACR 1,95±1,71 damage) were included into the study.
Antibodies to XO (anti-XO), ADA (anti-ADA) and ADC (anti-ADC) were determined in the procedure of indirect ELISA-test using the appropriate immobilized enzyme as antigen array [4]. Positive results were considered greater than 2 standard deviations of parameters obtained during the examination of healthy persons (for anti-XO> 0,097 IU; for anti-ADA> 0,112 IU; for anti-ADK> 0.470 U).
b2-glycoprotein-I-dependent antiphospholipid antibody (aPL) class IgM and IgG were determined using a commercial test kit «Anti-Phospholipid Screen IgG / IgM» (Orgentec). In the group of healthy individuals aPL levels of IgG / IgM does not exceed 10 GPL / MPL-U / ml.
Results.
On admission to hospital treatment (general group) anti-XO were detected in 53.3%, anti- ADA - at 53.3%, and anti-ADK - in 46.7% of patients with SLE.
Statistically significant correlations between the presence of the studied antibodies and clinical and laboratory parameters of SLE have been noticed. A direct correlation of antibody levels to indices of SLE activity (for anti-XO: SLEDAI r = 0,322, p = 0,016; ECLAM r = 0,331, p = 0.013; for anti-ADA: SLEDAI r = 0,318, p = 0,014; ECLAM r = 0.329, p = 0.011; for anti- ADK: SLEDAI r = 0,422, p = <0,001; ECLAM r = 0,502, p = <0.0005) and damage index (SLICC / ACR; for anti-XO r = 0,287, p = 0.029; for anti-ADA r = 0,284, p = 0.026) could indicate a close relation to the processes of the activity of SLE autoantibodies.
The inverse correlation of the level of anti-XO and hemoglobin level (r = - 0,286, p = 0.042), the number of lymphocytes (r = - 0,29, p = 0.033), and platelets (r = -0,308, p = 0.028) may be indicative of the direct activity of autoantibodies in blood cells. Also, a direct correlation between antibody level and the level of the CIC was observed (for anti-XO: r = 0.297, p = 0.024; for anti-ADK: r = 0.327, p = 0.021), aPL IgG (for anti-KO: r = 0.482, p = 0.04).
Antibodies to IgG class phospholipids were detected in 25 (41.7%) patients with SLE, aPL IgM class were detected in 19 (31.7%) patients with SLE. It was noted that aPL IgG class (but not aPL IgM class) more and a higher titer were observed in patients positive for the presence of antibody to ADA than in SLE patients negative for those antibodies (p = 0.029). A combined detection of anti-ADA and aPL in patients with SLE is associated with cytopenia (p = 0.019, Fisher's exact test).
The study of the immunological activity of key enzymes of adenine branch of the PM (XO, ADA, ADC) in groups of SLE patients with severe organ lesions suggests the activation of non-adenasine exchange mechanism of adenine nucleotides, which is a compensatory response to the preferential activation of enzyme units of inosine branch of the PM and a possible activation of enzymes of guanine purine degradation pathways and activation of ADC [5].
Conclusions.
Methods of immunoassay determining the level of antibodies to enzymes PM based on immobilized forms of enzymes as an antigen array were developed. The methods are available for use in clinical laboratories as an additional test in complex diagnostics of SLE in order to characterize the activity of the pathological process and certain clinical forms of the disease (the presence of antiphospholipid syndrome in SLE).
Список литературы
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