IgA- and insulin-containing (C3-fixing) circulating immune complexes in diabetes mellitus

Immunological responses to exogenous insulin

Regardless of purity and origin, therapeutic insulins continue to be immunogenic in humans. However, severe immunological complications occur rarely, and less severe events affect a small minority of patients. Insulin autoantibodies (IAAs) may be detectable in insulin-naive individuals who have a high likelihood of developing type 1 diabetes or in patients who have had viral disorders, have been treated with various drugs, or have autoimmune disorders or paraneoplastic syndromes. This suggests that under certain circumstances, immune tolerance to insulin can be overcome. Factors that can lead to more or less susceptibility to humoral responses to exogenous insulin include the recipient's immune response genes, age, the presence of sufficient circulating autologous insulin, and the site of insulin delivery. Little proof exists, however, that the development of insulin antibodies (IAs) to exogenous insulin therapy affects integrated glucose control, insulin dose requirements, and incidence of hypoglycemia, or contributes to beta-cell failure or to long-term complications of diabetes. Studies in which pregnant women with diabetes were monitored for glycemic control argue against a connection between IAs and fetal risk. Although studies have shown increased levels of immune complexes in patients with diabetic microangiopathic complications, these immune complexes often do not contain insulin or IAs, and insulin administration does not contribute to their formation. The majority of studies have shown no relationship between IAs and diabetic angiopathic complications, including nephropathy, retinopathy, and neuropathy. With the advent of novel insulin formulations and delivery systems, such as insulin pumps and inhaled insulin, examination of these issues is increasingly relevant.

Pathogenesis of autoimmune diseases associated with 8.1 ancestral haplotype: a genetically determined defect of C4 influences immunological parameters of healthy carriers of the haplotype

Subjects with certain HLA alleles have a higher risk of specific autoimmune diseases than those without these alleles. The 8.1 ancestral haplotype (AH) is a common Caucasoid haplotype carried by most people who type for HLA-B8,DR3. It is unique in its association with a wide range of immunopathological diseases. To gain insight into the identification of the mechanism(s) of disease susceptibility of 8.1 AH carriers, we have investigated the prevalence of circulating immune complexes and non-organ-specific autoantibodies in healthy carriers of the haplotype. The results show that carriers of 8.1 AH display both a significant increased prevalence of immune complexes and higher titers of anti-nuclear autoantibodies. This AH carries a single segment characterized by no C4A gene. This null allele does not code for a functional C4A protein that likely plays an anti-inflammatory role being specialized in the opsonization and immunoclearance processes. So, this genetic defect has been claimed to allow that an increased production of autoantibodies directed vs. cells that have undergone apoptosis and are not efficiently disposed because a reduced antigenic clearance. The results obtained in the present study fit very well with this hypothesis. In the AH carriers the simultaneous high setting of tumor necrosis factor (TNF)-alpha may supply the autoantigens (providing an excess of apoptotic cells) that drive the autoimmune response. In conclusion, the C4 defect associated to the increased spontaneous release of TNF-alpha, modifying a certain number of immunological parameter may be the most characterizing feature of the 8.1 AH. In the majority of individuals, an autoimmune response clinically relevant will develop only in the presence of other immunological abnormalities.

Insulin binds to glucagon forming a complex that is hyper-antigenic and inducing complementary antibodies having an idiotype-antiidiotype relationship

We demonstrate using physico-chemical techniques that insulin binds to glucagon with a Kd of 0.89 micromolar. While such binding is of little significance physiologically, it has important immunological consequences. Hormone binding is mirrored by specific binding between insulin antibody and glucagon antibody to form idiotype-antiidiotype complexes observable by Ouchterlony immunodiffusion and ELISA. These complexes may provide new insights into the formation of circulating immune complexes in diabetes. The insulin-glucagon complex is hyper-antigenic, inducing antibody production at concentrations that do not elicit immune responses from the individual hormones. The resulting immune response is not primarily against the individual hormones, but against the complex. In fact, all so-called insulin antibodies tested (rabbit, guinea pig, mouse and human) show substantially higher affinity for insulin-glucagon complex than for insulin alone, suggesting that this complex is the primary antigen in most, if not all, cases. These results lead to several testable predictions, including the possibility that glucagon antibody will bind to insulin receptors to cause type 2 (antibody mediated) insulin resistance.

Hypersialylated macromolecular serum immunoglobulin A1 in type 2 diabetes mellitus

OBJECTIVES

The origin of the elevation of serum immunoglobulin A1 (IgA1) in Type 2 diabetes mellitus (DM) is unsettled. The aim of this study was to address the carbohydrate changes of serum IgA1 from patients with Type 2 diabetes mellitus, as a possible cause of the elevation.

DESIGN AND METHODS

IgA1 was purified from sera of 6 DM patients and 4 healthy matched controls by using highly acetylated-Sepharose 6B, anti-IgA-agarose, and jacalin-agarose columns, and further separated into jacalin low-affinity, medium, and high-affinity fractions. Hinge and Fc fragments from native IgA1 were obtained and analyzed by using Sambucus nigra, Maackia amurensis, Arachis hypogaea, Erythrina cristagalli, and Ricinus communis lectins.

RESULTS

The jacalin high-affinity fraction, mostly constituted by macromolecular IgA1, was more abundant in DM patients than in controls and also more reactive to Sambucus nigra, and Maackia amurensis lectins.

CONCLUSIONS

Macromolecular serum IgA1 from DM patients is hypersialylated and this probably contributes to the high level of IgA1 in DM patients.

Significance of high levels of serum IgA and IgA-class circulating immune complexes (IgA-CIC) in patients with non-insulin-dependent diabetes mellitus

Significance of serum IgA and IgA-class circulating immune complexes (IgA-CIC) elevation in patients with non-insulin-dependent diabetes mellitus (NIDDM) was described. Seventeen patients with NIDDM and 17 patients with diffuse mesangial proliferative glomerulonephritis without deposition of IgA (DPGN) as controls were examined. The levels of serum IgA in patients with NIDDM were significantly higher than those in patients with DPGN (p < or = 0.01). The levels of IgA-CIC in patients with NIDDM were also significantly higher than those in patients with DPGN (p < or = 0.01). Production of IgA derived from B cells and the proportion of IgA bearing B cells in patients with NIDDM were not significantly higher than those in patients with DPGN. Furthermore, the levels of IgA in pharyngeal washings from diabetic patients were not significantly higher than those for DPGN patients. Duration of diabetes, the level of HbA1c, and the presence of hypertension, microalbuminuria, or retinopathy showed no significant correlations with the levels of serum IgA or IgA-CIC in patients with NIDDM. It was postulated that the elevations of serum IgA and IgA-CIC were based on subclinical infection of the mucosa and/or deterioration of IgA clearance in patients with NIDDM.

Nerve conduction velocity and circulating immunocomplexes in type 1 diabetic children

There is evidence from several laboratories of an increased prevalence of circulating immuno-complexes (CIC) in diabetic patients. It has also been suggested that CIC are pathogenetically related to chronic diabetic complications. The aim of this study was to assess peripheral nerve function in children with Type 1 diabetes and to evaluate the relationship between the neurophysiological abnormalities and the possible presence of CIC. The investigation was carried out in 25 Type 1 diabetic patients ranging in age from 7-19 years and in 20 normal controls. Neurophysiological assessment was performed to evaluate motor and sensory conduction velocity on median and tibial nerves. IgG-CIC were detected by the solid-phase C1q-binding and anti-C3 enzyme immuno-assay. The results of this study showed a greater slowing of median motor and sensory and tibial sensory conduction velocities in patients with CIC with respect to the patients without CIC, suggesting a possible role of immunological factors in the pathogenesis of diabetic neuropathy.

Immune complex-mediated inhibition of lymphocyte Fc-gamma receptors in the plasma of patients with type 1 (insulin-dependent) diabetes mellitus: association with anti-ssDNA antibodies

Sera of 43 patients with type 1 (insulin-dependent) diabetes and from 42 normal subjects were examined for the presence of Fc-gamma receptor-blocking IgG immune complexes, detected by EA rosette inhibition, and for the presence of anti-ssDNA antibodies by ELISA. Forty-four percent of diabetic patients had levels of inhibition above the upper limit of normality in comparison to 7% of normal controls. Anti-ssDNA antibodies were found in the sera of 14 out of 43 diabetic patients. Ten out of 14 anti-ssDNA positive patients (71.5%) had inhibition levels above the upper limit of normality in comparison to 9 out of 29 (31%) of the anti-ssDNA negative population. The difference was statistically significant (P less than 0.005). Levels of EA rosette inhibition were found to be high in patients with duration of diabetes of less than 2 years and correlated with high prevalence of anti-ssDNA antibodies. The percentage of EA rosette inhibition was found not to correlate with the levels of C1q-binding immune complexes, suggesting that immune complexes detected by EA rosette inhibition may belong to a pool of noncomplement-fixing immune complexes. The possible role of immune complexes with autoantibodies anti-ssDNA in the mechanism triggering and perpetuating autoimmune phenomena in diabetes is discussed.

C3-containing serum immune complexes in patients with systemic lupus erythematosus: correlation to disease activity and comparison with other rheumatic diseases

Although testing for circulating immune complexes (CIC) is regarded as a useful, complementary, laboratory parameter in the differential diagnosis and management of immune complex-induced vasculitis syndromes, there is still an uncertainty with regard to assay systems used for the demonstrated of soluble immune complexes. This is partly due to difficulties in the reproducibility, handling and principle limitations of available test systems for the assessment of soluble immune complexes in body fluids. In the present communication a modification of the anti-C3 test for the determination of CIC was developed using nitrocellulose as a solid phase matrix. IgG-, IgA- and IgM-containing CIC were determined and quantified using standard immune complex preparations. When 39 sera of SLE patients, 12 sera of patients with vasculitis syndromes, 10 sera of rheumatoid arthritis patients and 11 sera of patients with ankylosing spondylitis were tested, predominantly IgG-containing CIC could be demonstrated. Only in SLE patients was a significant amount of other immunoglobulin isotypes detected in CIC. In these patients a significant difference of IgG-containing CIC levels was found with regard to patients with high and low disease activity (P less than 0.0001). A significant correlation was also established between IgG-containing CIC and anti-dsDNA antibodies (P less than 0.001). In a longitudinal study the isotypes in the isolated CIC were found to be constant.

Association of serum IgA antibodies to milk antigens with severe atherosclerosis

The presence of antibodies of the IgA class against dietary antigens (bovine IgG (BGG), beta-lactoglobulin, casein, alpha-lactalbumin and xanthine oxidase, chicken ovalbumin and crude gliadin) was checked in the sera of 23 severely atherosclerotic subjects (ATS) and 20 highly selected controls (C). In these subjects an association between serum IgA levels and atherosclerosis had previously been shown. Determinations were performed by a micro-ELISA method and results were expressed as absorbances at 405 nm x 1000. Higher levels of IgA antibodies were found in ATS with respect to C against beta-lactoglobulin (respectively, 113.4 +/- 152.4 (1 SD) vs. 40.0 +/- 34.2; P less than 0.005) and casein (69.8 +/- 35.5 vs. 52.4 +/- 27.5; P less than 0.05). There was no difference in IgG and IgM against these 2 proteins between the 2 groups. Significant differences of prevalence of IgA antibodies were found for the following antigens: beta-lactoglobulin (4 C and 16 ATS over the limit value of 51; P less than 0.002), xanthine oxidase (1 C and 9 ATS over 289; P less than 0.01), BGG (7 C and 17 ATS over 87; P less than 0.02) and casein (5 C and 14 ATS over 60; P less than 0.02). These data suggest an association between anti-milk IgA antibodies and atherosclerosis. Its relevance and significance deserves further investigation.

Immunological aspects of diabetes mellitus: prospects for pharmacological modification

It is now well known that insulin-dependent diabetes is a chronic progressive autoimmune disease. The prolonged prediabetic phase of progressive beta-cell dysfunction is associated with immunological abnormalities. A prediabetic period is suggested by the appearance of islet cell antibodies, anti-insulin antibodies, and anti-insulin receptor antibodies. The existence of activated T lymphocytes and abnormal T cell subsets are also other markers. There is still no concensus about the use of the immunosuppression superimposed upon conventional insulin therapy in early diagnosed IDDM and the follow-up of the relatives of IDDM patients who share the genetic predisposition and serological markers for the risk of future onset of IDDM. Treatment in the prodromal period cannot be justified because a link between the disease and early markers such as ICA has not been established with certainty (Diabetes Research Program NIH, 1983). Many immunopharmacological manipulations were reported to be effective in animal models. However, most of them are not readily applied to human subjects. Moreover, IDDM patients are now believed to be heterogeneous, with a complex genetic background. HLA-DR, and more recently DQ, are closely related to the genetic predisposition to IDDM but those genes are not themselves diabetogenic. The contribution of autoimmunity does not appear to be uniform, and in some cases, the contribution of virus is considered more important. There is a lack of a marker for the future onset of IDDM. ICA and ICSA were found after mumps infection, but the existence of those autoantibodies and even the co-existence of HLA-DR3 do not always indicate the future trend to insulin dependency. More precise markers will be disclosed through the biochemical analysis of the target antigens on pancreatic beta-cell for islet antibodies and effector T cells. Much safer and more effective immunopharmacological treatment will be developed through animal experimentation using rat and mouse models. The recent development and interest in this field will further facilitate the attainment of the goal for the complete prevention of IDDM.

Comparative studies on immunoglobulins, complement component (C3), albumin, and immunoglobulin A-containing circulating immune complexes in serum and bile of patients with biliary obstruction

We measured the concentrations of IgA, IgG, IgM, secretory IgA, albumin, complement component (C3), and IgA-containing circulating immune complex (IgA-CIC) in the serum and bile of patients with biliary obstruction. The bile-to-serum (BS) ratio of the concentrations of albumin and IgG increased with the increase in total serum bilirubin. This indicates that the permeability from blood to bile increases with the degree of biliary obstruction, and the blood-bile barrier function breaks down. The BS ratios of IgA and IgM, which are selectively secreted into bile, did not show a significant correlation with total serum bilirubin. The index of the BS ratio to the BS ratio of albumin (BS/BS-Alb index) of IgA and IgM was significantly larger than that of IgG. This indicates that the selective transport of IgA and IgM into bile is present even in patients with obstructive jaundice. Since the BS/BS-Alb index of C3 is larger than that of IgG, and the SGOT correlated directly with the BS ratio of C3, some of the C3 in bile may come from damaged hepatocytes.

Circulating immune complex, endotoxin, and biliary infection in patients with biliary obstruction

Immunoglobulin A-containing circulating immune complexes, immunoglobulin G-containing circulating immune complexes, and endotoxin were measured in the sera of patients with obstructive jaundice. The bile of patients with percutaneous transhepatic biliary drainage was also cultured for bacteriologic studies. There was a significantly positive correlation between the endotoxin levels and both immunoglobulin A-containing circulating immune complex and immunoglobulin G-containing circulating immune complex. The endotoxin levels of the patients with gram-negative infections were significantly increased compared with those of the patients with sterile cultures. The immunoglobulin G-containing circulating immune complex levels of the patients with bacteria in bile were significantly increased compared with those of the patients with sterile cultures. The immunoglobulin A-containing circulating immune complex levels of the patients with bacteria in bile were slightly increased, but the difference did not reach statistical significance. These results indicate that one of the causes of increased circulating immune complex levels may be endotoxemia in combination with biliary infection in patients with biliary obstruction.

High levels of IgA-containing circulating immune complex and secretory IgA in Kawasaki disease

Sera of patients with Kawasaki disease were studied for the levels of IgA-containing (C3-fixing) circulating immune complexes (IgA-CIC), IgG-containing (IgG-)CIC, total IgA, secretory IgA, and complement component (C3) by means of enzyme-linked immunosorbent assays or single radial immunodiffusion methods. There was significantly high level of IgA-CIC, but not IgG-CIC. The levels of total IgA, secretory IgA, and C3 were significantly elevated. Significantly high levels of secretory IgA were found in 22 (51%) of 43 patients. The proportion of secretory IgA to total IgA also increased. These abnormalities in the IgA system may play a role in Kawasaki disease.

Circulating immune complexes containing bovine insulin in a patient with systemic allergic manifestations

A woman treated for 15 days with bovine insulin for gestational diabetes presented with severe urticaria of the chest and back, distant from the injection site. She had neither local reaction nor general manifestations. Replacement of bovine NPH insulin by biosynthetic human NPH was followed by regression of urticaria. We isolated the circulating immune complex (CIC), mainly of IgG class, from the patient's serum. It disappeared when bovine insulin administration had been ceased for 48 h. There were no specific IgE-insulin-antibodies. The IgG-CIC were dissociated. Insulin was identified by RIA in the CIC. Insulin characterization was carried out by high-performance liquid chromatography (HPLC), which showed that the insulin in the complexes was injected bovine insulin.

Analysis of serum and synovial fluid IgA in Reiter's syndrome and reactive arthritis

The presumed antecedent infection which precedes Reiter's syndrome and reactive arthritis is frequently across a mucosal surface, and IgA immune responses may play a role in this process. Twelve of 29 patients with these conditions demonstrated elevation in serum IgA levels, and serum IgA levels in the postdysentery group (mean 3.21 g/liter +/- 1.27) were higher (P less than 0.01) than those in the posturethritis group (mean 2.40 g/liter +/- 0.80). In 10 of the 12 patients, IgA was the only immunoglobulin increased. There was no evidence of activation of complement in serum or synovial fluid. Using a complement-dependent assay, we were unable to demonstrate circulating IgA immune complexes. Sucrose density gradient ultracentrifugation analysis was used to assess IgA immune complexes in a non-complement-dependent manner. IgA of 11s was in fact demonstrated by this technique but appeared to be polymeric IgA on the basis of specific binding of secretory component and resistance to acid dissociation. IgA rheumatoid factor was not present. Synovial fluid revealed levels of polymeric IgA higher (mean 56.7% +/- 12.9) than did serum (23.7% +/- 13.9, P less than 0.001) despite higher levels of total IgA in serum than in synovial fluid (synovial fluid:serum ratio of IgA, mean 0.53 +/- 0.11). Although elevation in serum IgA in postdysenteric arthropathies suggests mucosal acquisition of antigen, the study does not implicate IgA circulating immune complexes in the pathogenesis of these diseases.

A solid-phase anti-C3 assay for detection of immune complexes in six distinguished forms

A solid-phase anti-C3 assay detecting immune complexes associated with C3 fragments is described. Two monoclonal antibodies against C3 fragments are used; one recognizes an epitope expressed on C3b, C3c and C3i, the other recognizes an epitope expressed on C3dg and iC3b. Combining these monoclonal anti-C3s with antibodies against class-specific immunoglobulins in enzyme-linked immunosorbent assay (ELISA), immune complexes (ICs) are detected in six distinguished forms; C3b-IgG-IC, iC3b/C3dg-IgG-IC, C3b-IgA-IC, iC3b/C3dg-IgA-IC, C3b-IgM-IC and iC3b/C3dg-IgM-IC. About three-fourths of the plasma samples from patients with active SLE or IgA-nephritis were found positive in one or more types of ICs. IgA-type ICs were found very frequently in patients with autoimmune or renal diseases.

Clinical significance of U1-RNP immune complexes in mixed connective tissue disease and systemic lupus erythematosus

We measured U1-RNP: anti-U1-RNP immune complexes (U1-RNP ICs) in patients with mixed connective tissue disease (MCTD) and systemic lupus erythematosus (SLE) to examine the clinical significance of circulating U1-RNP ICs. The level of U1-RNP ICs in 11 patients with MCTD was significantly higher than that in 22 normal subjects and there was a close correlation between the level of U1-RNP ICs and the clinical disease activity index of MCTD. In contrast, the level of U1-RNP ICs in 31 patients with SLE was not significantly higher than that in normal subjects and that was not correlated with the clinical disease activity index of SLE or the renal histologic activity index of lupus nephritis. We conclude that U1-RNP ICs are present in sera of patients with MCTD and SLE, and that the level of U1-RNP ICs may be closely associated with clinical disease activity in patients with MCTD.

A solid-phase radioimmunoassay for the detection of nRNP immune complexes

We developed a solid-phase radioimmunoassay for complement (C)-fixing nuclear ribonucleoprotein (nRNP):anti-nRNP immune complexes (nRNP ICs). The assay was based on the ability of the C-fixing nRNP ICs to bind strongly to immobilized F(ab')2 anti-C3. The extent of binding was quantified by incubating the C-fixing nRNP ICs bound to anti-C3 with 125I-labeled anti-nRNP-specific IgG. The interaction between anti-C3 and C-fixing nRNP ICs was rapid, time- and concentration-dependent and sensitive over a broad range of nRNP IC concentrations in an antigen-antibody ratio of 8 : 1 (9.8-5000 ng of human aggregated IgG equivalent per ml). We found that the assay also detected an immunoreactive U1-RNP antigen in Sm : anti-Sm immune complexes but did not detect SSA : anti-SSA immune complexes. The assay was preliminary applied for serum samples obtained from patients with mixed connective tissue disease (MCTD), and elevated concentrations of nRNP immune complexes were found in 3 out of 5 patients with MCTD. This assay appears to be applicable to the detection and quantification of circulating nRNP ICs in patients with MCTD.

Detection of circulating Yersinia-immunoglobulin complexes by enzyme immunoassay (EIA)

An enzyme immunoassay (EIA) was developed for the detection of Yersinia-immunoglobulin complexes of known Ig class. Immune complexes (ICs) were attached to polystyrene microtiter plates by rabbit anti-human immunoglobulins, and the existence of Yersinia enterocolitica O:3 antigens was demonstrated using Fab fragments of alkaline phosphatase (AP)-conjugated antibody against the same serotype. Simultaneous binding of Yersinia antigens and immunoglobulins was a prerequisite for the detection of ICs. The method will be valuable for research into the immunopathogenetic mechanisms leading to reactive arthritis after Yersinia infection.

Relationship between secretory IgA, IgA-containing (C3-fixing) circulating immune complexes, and complement components (C3, C4) in patients with obstructive jaundice

Serum secretory IgA, IgA-containing circulating immune complexes (IgA-CIC), complement components, and major immunoglobulins were measured in patients with biliary tract stones and/or tumors of the biliary tract or pancreas. The levels of secretory IgA and total IgA were increased in patients with and without obstructive jaundice. The levels of both C3 and C4 were significantly higher in patients with or without obstructive jaundice than in healthy controls. In patients with obstructive jaundice the increased levels of secretory IgA, total IgA, and IgA-CIC were correlated with the increase of C3 but not with that of C4.

Are the vascular complications of diabetes mellitus preceded by an altered thromboxane/prostacyclin plasmatic ratio?

Although many data regarding the biosynthesis of thromboxane A2 and prostacyclin in diabetes mellitus have recently appeared in the literature, it is not clear whether an imbalance between the generation of the two prostaglandins might be connected to the vascular complications of diabetes. In the present review we have tried to emphasize the most significant aspects of these studies and we have focused on alterations of platelet prostacyclin receptors and on the effects of circulating immune complexes on platelets of diabetics. It is likely that studies on the release of platelet derived growth factor as well as more precise definitions of its action on vessel wall cells leading to a massive release of prostacyclin, will permit us to ascertain whether an alteration in prostaglandin ratio is linked to the genesis of the vascular complications in diabetics.

Quantitative immunoassay for IgA class circulating immune complexes using solid phase Facb fragment of anti-C3

A quantitative assay of IgA class circulating immune complexes (IgA-CIC) by a solid phase anti-C3 enzyme immunoassay (anti-C3 EIA) is described. A stable and reproducible standard for determination of IgA-CIC was prepared successfully by chemical binding of complement C3 to human serum IgA. Two of 27 sera from patients with systemic lupus erythematosus (SLE), however, contained high concentrations of IgA class anti-F(ab')2 antibodies that caused false positive results when the F(ab')2 of anti-C3 was used for EIA. Solid phase Facb of anti-C3 was found to eliminate the false positive results caused by IgA class anti-F(ab')2 and IgA class rheumatoid factor. Good reproducibility and recovery were observed with this Facb anti-C3 EIA using the IgA-C3, a stable standard material, and so this method should be useful clinically in elucidating the role of IgA-CIC.

Contribution of secretory IgA, polymeric IgA and IgA/secretory component-containing circulating immune complexes to the serum hyper-IgA in diabetes mellitus

The relative contribution of secretory IgA, monomeric and polymeric IgA and IgA/secretory component-containing immune complexes was investigated in sera of diabetic patients. Secretory IgA and immune complexes containing IgA and secretory component seem to participate in the hyper-IgA of patients with Type 2 (non-insulin-dependent) diabetes only, suggesting an altered hepatic clearance via secretory component receptors on hepatocytes. In Type 1 (insulin-dependent) diabetes, the high serum IgA levels might be explained by an increase in IgA production in response to antigenic stimuli. Evidence is also accumulated that immune complexes containing IgA of mucosal origin may be involved in microangiopathy production in Type 2 diabetes.