New Insights Into The Role Of IgG Anti-dsDNA Antibody And Calreticulin In Lupus Nephritis

Backgroud Systemic lupus erythematosus (SLE)is a prototypic autoimmune disease characterized by the production of antibodies to components of the cell nucleus in association with a diverse array of clinical manifestations. Defective immune regulatory mechanisms, such as the clearance of apoptotic cells and immune complexes, are important contributors to the development of SLE. The loss of immune tolerance, increased antigenic load, excess T cell help, defective B cell suppression, and the shifting of T helper 1 (Th1) to Th2 immune responses leads to B cell hyperactivity and the production of pathogenic autoantibodies. Finally, certain environmental factors are probably required to trigger the disease. but the underlying mechanisms are unclear.Lupus nephritis is a major complication of systemic lupus erythematosus and is associated with a hige rate of morbidity and mortality.while many different immunologic and nonimmunologic factors contribute to disease expression in lupus nephritis,a large body of evidence suggests that the production of anti-DNA antibodies and the formation of glomerular immune deposits are important initial events in the pathogenesis of the disease.The precise mechanisms by which autoantibodies form immune deposits have been an area of much debate.three theories have been propose:1)deposition of circulating immune complexs;2)direct binding to endogenous renal antigens;3)direct binding to endogenous antigens localized within the kidney .these are not mutually exclusive and all likely contribute to some extent at various times during disease. But Rekvig et al found that anti-dsDNA antibody are common in patients with SLE, but not all patients with positive anti-dsDNA antibody can develop LN,and the relationship of the autoantibody to disease is not straightforward since serum levels do no always correlate with disease activity.and which is needed a new sight to reveal the pathogenic of LN. Another researches found some subsets of IgG anti-dsDNA antibody can enter cells,and some of these have been shown to alter cell function,and this intracellular penetration of anti-dsDNA antibodis may play important role in the pathogenicity of LN.IgG anti-dsDNA antibody can enter not only glomerulus cells,but also renal tubule,hepatic cell,neuron cell, myofibroblast and monocytes,firstly these antibodies connect with cell surface,then enter cell cytoplasm or location on cell nucleus,and this location need the help of membrane receptor,there are many kinds of membrane receptor of IgG anti-dsDNA antibody,which can contribute the penetration.some researcher found CRT is one of the membrane receptor of IgG anti-dsDNA antibody which can mediate the penetration.Thus, we make a hypothesis that IgG anti-dsDNA antibody in SLE patients can penetrate renal biopsy which resluts in renal damage,may because of the high levels of IgG anti-dsDNA antibody and the high expression of CRT in renal biopsy.then this different induce to SLE patients with positive IgG anti-dsDNA antibody can develop LN,and some patients do not have renal damage.Objective To compare the distribution of serum IgG anti-dsDNA antibody and its subsets using enzyme-linked immunosorbent assay among healthy controls,LN patients and SLE patients without renal damage,and to analyse the relationship between IgG anti-dsDNA antibody with lupus nephritis,and to analyse the relationship between four serum IgG anti-dsDNA antibody subclasses with disease activity,and to discribe the distribution of IgG subsets and CRT in renal biopsy. Methods SLE patients were selected from two hospital,and then divided into two groups that were LN group and SLE not LN group,and normal healthy volunteers were recruited as controls.general information and the data of renal damage were collected by self-designed questionnaire containing SLEDAI,AI,CI.ELISA was used to detect the levels of IgG anti-dsDNA antibody and its subsets,kidney biospy specimens of patients with LN were analysed for IgG subclass and CRT deposition.Results Patients with SLE (n=60)had a significantly higher level of chronic IgG anti-dsDNA antibody compared to healthy controls(n=60)(χ2=31.16,P<0.001),but that was no significant difference between LN group (n=28)and SLE not LN group (n=32)(χ2=0.021,P=0.885).In 32 patients with SLE not LN,11 had positive IgG1 anti-dsDNA antibody,1 had positive IgG2 anti-dsDNA antibody,and 8 had positive IgG3 anti-dsDNA antibody,and that was 18,17,8,respectively.patients with LN had a significantly higher IgG1(χ2=5.35,P=0.021) and IgG2 (χ2=5.24,P=0.022)compared to patients with SLE no LN,but this was no significant diffferent in IgG3(χ2=0.09,P=0.755),and IgG4 was not detected in both groups.In all SLE patients(n=60),active patients (n=36)had a significantly higher IgG anti-dsDNA antibody compared to nonactive patients(n=24)(χ2=4.57,P=0.033) .the analysis of subsets of IgG antibody suggested that active patients (n=36)had a significantly higher IgG2 anti-dsDNA antibody compared to nonactive patients(n=24)(χ2=4.05,P=0.044).In 32 patients with SLE no LN, active patients (n=16)had not significantly higher IgG anti-dsDNA antibody subclasses compared to nonactive patient(sn=16).while in 28 patients with LN, active patients (n=20)had a significantly higher IgG2 anti-dsDNA antibody compared to nonactive patients(χ2=5.99,P=0.014). Type IV was the most common type of LN (39.3%),and type III(35.7%),II(17.9%) were the followings.The pecentage of WHO type III and IV LN in the patients with anti-dsDNA antibody positive was higher than that in the patients with anti-dsDNA antibody negative ,but the difference was no significance,which was similar in all of subclasses,the proteinuria,blood urine,azotemia in the patients with anti-dsDNA antibody positive was higher than that in the patients with anti-dsDNA antibody negative ,but only the difference of azotemia was significance,fourthemore,azotemia in the patients with IgG1 anti-dsDNA antibody positive was higher than that in the patients with anti-dsDNA antibody negative,and blood urine in the patients with IgG2 anti-dsDNA antibody positive was higher than that in the patients with anti-dsDNA antibody negative.There was a relationship between serum IgG anti-dsDNA antibody and active index (Spearman r = -0.464,P =0.017)and chronic index(Spearman r = -0.508, P =0.013),but further reseach suggested only IgG2 anti-dsDNA antibody had been related to active index.In kidney biopsies all IgG subclasses could be detected.No correlatioin was found between the relative amount of any of the IgG subclasses in the kidney biopsy and plasma levels of IgG antibody subclasses to anti-dsDNA.Compared to WHOI,II,WHO III,IV,V had high expression of CRT,and there was a correlation between CRT and anti-dsDNA antibody(Spearman r = -0.504, P =0.006),and active index of LN(Spearman r = 0.973, P <0.001),but no correlatioin was found between CRT and chronic index of LNConclusions IgG1 and IgG2 subclass antibodies to dsDNA were the predominant subclasses found in plasma of patients with LN,the frequent occurrence of a rise in IgG2 anti-dsDNA antibody in active LN patients suggests that IgG2 subclass antibodies have a particular pathophysiological role in lupus nephritis.not consistent correlation exist between pathological classification and clinical features of LN,anti-dsDNA antibody may be a relible paremeter of LN activity.The coaction of CRT and anti-daDNA antibody may play more important role in the pathogenicity of LN.