GAD-Reactive T Cells Were Mainly Detected in Autoimmune-Related Type 1 Diabetic Patients with HLA DR9

The Unfavorable Impact of DR9/DR9 Genotype on the Frequency and Quality of Partial Remission in Type 1 Diabetes

CONTEXT

Partial remission (PR) is a specific stage in type 1 diabetes (T1D). Although human leukocyte antigen (HLA) class II loci are the strongest genetic determinants in T1D, the relationship between PR and HLA remains unclear.

OBJECTIVE

To investigate the association between PR status and HLA genotypes in patients with T1D.

METHODS

A total of 237 patients with T1D were included. PR was defined according to C-peptide ≥300 pmol/L. The frequency of PR and peak C-peptide levels during remission phase were compared according to HLA status. Clinical characteristics including age of onset and diabetes autoantibodies were collected. All analyses were duplicated when subjects were divided into childhood- and adult-onset T1D.

RESULTS

The median follow-up time was 24 months, 65.8% (156/237) of patients with T1D went into PR. DR9/DR9 carriers had a lower PR rate (44.2% vs 70.6%, P = .001) and were less likely to enter PR (OR = 0.218, 95% CI 0.098-0.487, P < .001) than the non-DR9/DR9 carriers, observed in both childhood- and adult-onset T1D. Besides, the peak C-peptide level during PR phase was also lower in DR9/DR9 carriers, and more notable in adult-onset T1D. When compared with non-DR9/DR9 carriers, T1D with DR9/DR9 genotype presented an older age of onset and a lower positivity of zinc transporter 8 antibody (ZnT8A), and the lower trend of ZnT8A was only found in adult-onset T1D (P = .049).

CONCLUSION

Patients with T1D carrying susceptible DR9/DR9 are less prone to undergo PR. Additionally, the recovery extent of β-cell function during the PR phase tends to be lower in adults carrying DR9/DR9, which might be associated with ZnT8A.

Possible involvement of autoimmunity in fulminant type 1 diabetes

Fulminant type 1 diabetes (FT1D) is characterized by a relatively low HbA1c level at the onset, despite the abrupt occurrence of marked hyperglycemia with ketosis or ketoacidosis. The initial symptoms/findings are flu-like, absence of islet-associated autoantibodies, and a drastic decrease in β-cells and α-cells, which strongly suggest the involvement of a viral infection. In fact, we successfully demonstrated that a FT1D-like phenotype can be reproduced in encephalomyocarditis virus-induced diabetes murine model. However, there is a discussion on the possible involvement of autoimmunity rather than viral infection as the underlying cause of FT1D. For example, HLA-DRB1*04:05, a susceptible antigen of type 1A diabetes, is reportedly associated with FT1D in Japan. Moreover, anti-glutamic acid decarboxylase antibody is reportedly detected in ~ 5% of the patients. Additionally, half of the patients with anti-programmed cell death-1 therapy-related type 1 diabetes fulfilled the criteria of the disease. These findings suggest that islet-associated autoimmunity can partially contribute to the development of FT1D. Furthermore, using nonobese diabetic mice with reduced regulatory T-cell (Treg) numbers, we found that a human FT1D-like phenotype can be induced by islet-associated autoimmunity through collaboration between innate immunity (macrophages and/or natural killer cells) and acquired immunity (predominantly cytotoxic CD8⁺ T cells) in genetically predisposed individuals of autoimmune type 1 diabetes with low Tregs or Treg dysfunction. To clarify greater details regarding the association of autoimmunity in the pathogenesis of FT1D, further studies using suitable animal models and accumulation of the relevant patients are required.

Distinct Phenotypes of Islet Antigen-Specific CD4+ T Cells Among the 3 Subtypes of Type 1 Diabetes

CONTEXT

Type 1 diabetes (T1D) is classified into 3 subtypes: acute-onset (AT1D), slowly progressive (SP1D), and fulminant (FT1D). The differences in the type of cellular autoimmunity within each subtype remain largely undetermined.

OBJECTIVE

To determine the type and frequency of islet antigen-specific CD4+ T cells in each subtype of T1D.

PARTICIPANTS

Twenty patients with AT1D, 17 with SP1D, 18 with FT1D, and 17 persons without diabetes (ND).

METHODS

We performed an integrated assay to determine cellular immune responses and T-cell repertoires specific for islet antigens. This assay included an ex vivo assay involving a 48-hour stimulation of peripheral blood mononuclear cells with antigen peptides and an expansion assay involving intracytoplasmic cytokine analysis.

RESULTS

The results of the ex vivo assay indicated that glutamic acid decarboxylase 65 (GAD65)-specific interleukin-6 and interferon-inducible protein-10 (IP-10) responses and preproinsulin (PPI)-specific IP-10 responses were significantly upregulated in AT1D compared with those of ND. Furthermore, GAD65- and PPI-specific granulocyte colony-stimulating factor responses were significantly upregulated in FT1D. Expansion assay revealed that GAD65- and PPI-specific CD4+ T cells were skewed toward a type 1 helper T (Th1)- cell phenotype in AT1D, whereas GAD65-specific Th2 cells were prevalent in SP1D. GAD65-specific Th1 cells were more abundant in SP1D with human leukocyte antigen-DR9 than in SP1D without DR9. FT1D displayed significantly less type 1 regulatory T (Tr1) cells specific for all 4 antigens than ND.

CONCLUSIONS

The phenotypes of islet antigen-specific CD4+ T cells differed among the three T1D subtypes. These distinct T-cell phenotypes may be associated with the manner of progressive β-cell destruction.

Clinical and genetic characteristics of people with type 1 diabetes who have discrepancies in titers of anti-glutamic acid decarboxylase antibody measured by radioimmunoassay and enzyme-linked immunosorbent assay

AIMS/INTRODUCTION

The aim of the present study was to compare the clinical and genetic characteristics between people with type 1 diabetes who were positive and negative for autoantibodies against glutamic acid decarboxylase (GADA) measured by enzyme-linked immunosorbent assay (ELISA) with low-titer GADA measured by radioimmunoassay.

MATERIALS AND METHODS

Among Japanese people with type 1 diabetes in whom GADA were measured by both ELISA and radioimmunoassay, those who had low titers of GADA measured by radioimmunoassay (1.5-10 U/mL), regardless of positivity for GADA measured by ELISA, were studied. There were 65 participants with acute-onset type 1 diabetes and 30 participants with slowly progressive insulin-dependent diabetes mellitus. Clinical characteristics and human leukocyte antigen types were compared in ELISA-positive (≥5 U/mL) and ELISA-negative participants. Endogenous insulin secretion was evaluated by C-peptide index.

RESULTS

Among participants with slowly progressive insulin-dependent diabetes mellitus, postprandial C-peptide index was significantly higher in ELISA-negative participants than in ELISA-positive participants (r = 0.619, P = 0.002). Among 52 participants whose human leukocyte antigen typing was carried out, all of the participants with slowly progressive insulin-dependent diabetes mellitus who had DRB1*09:01 were positive by GADA-ELISA (P = 0.021). In acute-onset type 1 diabetes participants, there were no significant differences for the C-peptide index and human leukocyte antigen genotypes.

CONCLUSIONS

The difference in the positivity for GADA-ELISA might reflect cytotoxicity toward pancreatic β-cells and preservation of endogenous insulin secretion in people with slowly progressive insulin-dependent diabetes mellitus. We also suggest that the difference in the GADA-ELISA-specific epitope depends on the human leukocyte antigen genotype.

Clinical characteristics of anti-glutamic acid decarboxylase antibody-positive fulminant type 1 diabetes

This research aimed to examine the relationship between anti-glutamic acid decarboxylase antibody (GADA) titers and clinical parameters at onset and to clarify the association between clinical severity and GADA titers in GADA-positive fulminant type 1 diabetes. This cross-sectional observational study included 20 cases with GADA-positive fulminant type 1 diabetes (4 cases from our hospital and 16 from cases reported in the literature). The association between GADA titers and clinical parameters [age, sex, body weight, body mass index, period from appearance of any prodromal symptoms to diagnosis, period from development of hyperglycemic symptoms to diagnosis, GADA titer, HbA1c level, blood pH and HCO₃^- level, serum levels of ketone bodies and pancreatic exocrine enzymes] were analyzed. Spearman's rank correlation coefficient (r_s) was used for the correlation analysis. The results showed that there was a significant inverse correlation between GADA titers and the "period from appearance of any prodromal symptoms to diagnosis" (r_s = -0.559, p < 0.05). Moreover, GADA titers were inversely correlated with blood pH and HCO₃^- level (r_s = -0.576, p < 0.05, r_s = -0.578, p < 0.05, respectively), and positively correlated with serum levels of total ketone bodies, acetoacetate, and 3-hydroxybutyrate (r_s = 0.661, p < 0.05; r_s = 0.700, p < 0.05; and r_s = 0.782, p < 0.01, respectively). These findings suggest that higher GADA titers may be linked to more severe clinical severity of GADA-positive fulminant type 1 diabetes at onset. This association may be attributed to possible pre-existence of autoimmunity-related β-cell damage before the onset of fulminant type 1 diabetes.

Glutamic acid decarboxylase 65 and islet cell antigen 512/IA-2 autoantibodies in relation to human leukocyte antigen class II DR and DQ alleles and haplotypes in type 1 diabetes mellitus

The frequencies of autoantibodies against glutamic acid decarboxylase 65 (GAD65) and islet cell antigen (ICA) 512/IA-2 (512/IA-2) are functions of the specific human leukocyte antigen (HLA) in type 1 diabetes mellitus (T1D). We investigated the association of HLA class II (DR and DQ) alleles and haplotypes with the presence of GAD and IA-2 autoantibodies in T1D. Autoantibodies were tested in 88 Tunisian T1D patients and 112 age- and gender-matched normoglycemic control subjects by enzyme immunoassay. Among T1D patients, mean anti-GAD antibody titers were higher in the DRB1*030101 allele (P < 0.001), together with the DRB1*030101/DQB1*0201 (P < 0.001) and DRB1*040101/DQB1*0302 (P = 0.002) haplotypes, while lower anti-GAD titers were associated with the DRB1*070101 (P = 0.001) and DRB1*110101 (P < 0.001) alleles and DRB1*070101/DQB1*0201 (P = 0.001) and DRB1*110101/DQB1*030101 (P = 0.001) haplotypes. Mean anti-IA-2 antibody titers were higher in the DRB1*040101 allele (P = 0.007) and DRB1*040101/DQB1*0302 (P = 0.001) haplotypes but were lower in the DRB1*110101 allele (P = 0.010) and the DRB1*110101 (P < 0.001) and DRB1*110101/DQB1*030101 (P = 0.025) haplotypes. Multinomial regression analysis confirmed the positive association of DRB1*030101 and the negative association of DRB1*110101 and DQB1*030101, along with the DRB1*070101/DQB1*0201 and DRB1*110101/DQB1*030101 haplotypes, with anti-GAD levels. In contrast, only the DRB1*040101/DQB1*0302 haplotype was positively associated with altered anti-IA-2 titers. Increased GAD65 and IA-2 antibody positivity is differentially associated with select HLA class II alleles and haplotypes, confirming the heterogeneous nature of T1D.

The role of the CXCL10/CXCR3 system in type 1 diabetes

Despite intervention with insulin, type 1 diabetes gradually deteriorates the patients' quality of life. The disease is characterized by an immune-mediated destruction of pancreatic beta-cells. Its etiology, however, remains controversial. Some studies argue that glutamic acid decarboxylase (GAD) antigen and GAD-reactive T cells are critical players in the development of diabetes by affecting the Th cell balance. A T-helper 1 (Th1)-dominant immune response is considered to be important in beta-cell failure in both human and animal models of type 1 diabetes. The Th1-type chemokine, CXCL10, and its receptor, CXCR3, are involved not only in the immune response, but also in the suppression of beta-cell proliferation. Thus, understanding the CXCL10/CXCR3 system may be important for finding a cure. In this short review, we discuss the role of the CXCL10/CXCR3 system in type 1 diabetes and propose relevant treatment options.

The binding of antigenic peptides to HLA-DR is influenced by interactions between pocket 6 and pocket 9

Peptide binding to class II MHC protein is commonly viewed as a combination of discrete anchor residue preferences for pockets 1, 4, 6/7, and 9. However, previous studies have suggested cooperative effects during the peptide binding process. Investigation of the DRB1*0901 binding motif demonstrated a clear interaction between peptide binding pockets 6 and 9. In agreement with prior studies, pockets 1 and 4 exhibited clear binding preferences. Previously uncharacterized pockets 6 and 7 accommodated a wide variety of residues. However, although it was previously reported that pocket 9 is completely permissive, several substitutions at this position were unable to bind. Structural modeling revealed a probable interaction between pockets 6 and 9 through beta9Lys. Additional binding studies with doubly substituted peptides confirmed that the amino acid bound within pocket 6 profoundly influences the binding preferences for pocket 9 of DRB1*0901, causing complete permissiveness of pocket 9 when a small polar residue is anchored in pocket 6 but accepting relatively few residues when a basic residue is anchored in pocket 6. The beta9Lys residue is unique to DR9 alleles. However, similar studies with doubly substituted peptides confirmed an analogous interaction effect for DRA1/B1*0301, a beta9Glu allele. Accounting for this interaction resulted in improved epitope prediction. These findings provide a structural explanation for observations that an amino acid in one pocket can influence binding elsewhere in the MHC class II peptide binding groove.

Frequency of CTLA-4 gene CT60 polymorphism may not be affected by vitamin D receptor gene Bsm I polymorphism or HLA DR9 in autoimmune-related type 1 diabetes in the Japanese

One of the CTLA-4 SNPs, +6230G>A (CT60), has recently been reported to be related to susceptibility to type 1 diabetes and autoimmune thyroid disease. We have previously reported an association between acute-onset type 1 diabetes in Japanese and the Vitamin D receptor (VDR) gene Bsm I large B polymorphism, which is related to the Th1-type response. Moreover, we found a significant correlation between autoimmune-related type 1 diabetes with HLA DR9 and detection of GAD-reactive Th1 (T helper 1)-type cells. In the present article, we tried to clarify whether the frequency of one of the CTLA-4 SNPs, +6230G>A (CT60), is affected by the VDR gene Bsm I polymorphism or by HLA DR9 in Japanese type 1 diabetics. The frequency of the CT60 GG genotype did not appear to be affected by either the VDR gene Bsm I large B polymorphism or HLA DR9.