Stability of disease-associated antibody titers in pregnant women with type 1 diabetes with or without residual beta-cell function

Islet autoantigens: structure, function, localization, and regulation

Islet autoantigens associated with autoimmune type 1 diabetes (T1D) are expressed in pancreatic β cells, although many show wider patterns of expression in the neuroendocrine system. Within pancreatic β cells, every T1D autoantigen is in one way or another linked to the secretory pathway. Together, these autoantigens play diverse roles in glucose regulation, metabolism of biogenic amines, as well as the regulation, formation, and packaging of secretory granules. The mechanism(s) by which immune tolerance to islet-cell antigens is lost during the development of T1D, remains unclear. Antigenic peptide creation for immune presentation may potentially link to the secretory biology of β cells in a number of ways, including proteasomal digestion of misfolded products, exocytosis and endocytosis of cell-surface products, or antigen release from dying β cells during normal or pathological turnover. In this context, we evaluate the biochemical nature and immunogenicity of the major autoantigens in T1D including (pro)insulin, GAD65, ZnT8, IA2, and ICA69.

Danish children born with glutamic acid decarboxylase-65 and islet antigen-2 autoantibodies at birth had an increased risk to develop type 1 diabetes

OBJECTIVE

A large, population-based case-control cohort was used to test the hypothesis that glutamic acid decarboxylase-65 (GAD65) and islet antigen-2 autoantibodies (IA-2A) at birth predict type 1 diabetes.

DESIGN AND METHODS

The design was an individually matched case-control study of all Danish type 1 diabetes patients born between 1981 and 2002 and diagnosed before May 1 2004 (median age at diagnosis was 8.8 years). Dried blood spot samples collected 5 days after birth in the 1981-2002 birth cohorts and stored at -25 °C were identified from 2023 patients and from two matched controls (n = 4042). Birth data and information on parental age and diabetes were obtained from Danish registers. GAD65A and IA-2A were determined in a radiobinding assay. HLA-DQB1 alleles were analyzed by PCR using time-resolved fluorescence.

RESULTS

GAD65A and IA-2A were found in 70/2023 (3.5%) patients compared to 21/4042 (0.5%) controls resulting in a hazard ratio (HR) of 7.49 (P < 0.0001). The HR decreased to 4.55 but remained significant (P < 0.0003) after controlling for parental diabetes and HLA-DQB1 alleles. Conditional logistic regression analysis showed a HR of 2.55 (P < 0.0001) for every tenfold increase in the levels of GAD65A and IA-2A. This HR decreased to 1.93 but remained significant (P < 0.001) after controlling for parental diabetes and HLA-DQB1 alleles.

CONCLUSION

These data suggest that GAD65A and IA-2A positivity at birth are associated with an increased risk of developing type 1 diabetes in Danish children diagnosed between 1981 and 2004.

GAD65 autoantibodies and its role as biomarker of Type 1 diabetes and Latent Autoimmune Diabetes in Adults (LADA)

One of the hallmarks of autoimmune diabetes is the presence of adaptive responses directed to neuroendocrine proteins. One of these proteins is glutamic acid decarboxylase (GAD). While GAD is widely distributed in neuroendocrine tissues, its specific significance in diabetes has paralleled the advances in understanding humoral and cellular immunity in Type 1 diabetes (T1D) and in a subset of Type 2 diabetes (T2D), going from the seminal discoveries of islet autoantibodies to the development and standardization of bioassays as diagnostic tools, to studies on the structure of GAD and its antigenic determinants. GAD65 autoantibodies can accurately predict T1D development in combination with other surrogate humoral biomarkers and they are considered the most sensitive and specific biomarker which identifies a subset of clinically diagnosed T2D termed Latent Autoimmune Diabetes in Adults (LADA). We and others provided evidence indicating that GAD65 autoantibody detection should be part of the diagnostic assessment for clinically diagnosed T2DM mainly because it predicts the rate of progression to insulin requirement in patients affected by LADA. More recently GAD has been used as a "tolerogenic vaccine" to preserve beta cell function in autoimmune diabetes. While the results of Phase III clinical trials did not substantiate the earlier promise of Phase I and II trials, there are still many unanswered questions and approaches that need to be investigated in the applications of GAD in the therapy of T1D and LADA.

Pregnancy-induced rise in serum C-peptide concentrations in women with type 1 diabetes

OBJECTIVE

The purpose of this study was to investigate whether pregnancy induces increased insulin production as a marker of improved beta-cell function in women with long-term type 1 diabetes.

RESEARCH DESIGN AND METHODS

This was a prospective study of 90 consecutive pregnant women with type 1 diabetes. At 8, 14, 21, 27, and 33 weeks blood samples were drawn for measurements of A1C, C-peptide, and serum glucose. C-peptide (detection limit: 6 pmol/l) was considered stimulated at a corresponding serum glucose concentration >or=5.0 mmol/l. GAD antibody concentration was determined at 8 and 33 weeks in 35 women.

RESULTS

C-peptide concentrations gradually increased throughout pregnancy regardless of serum glucose concentrations in the 90 women with a median duration of diabetes of 17 years (range 1-36 years). Among 35 women with paired recordings of stimulated C-peptide, C-peptide production was detectable in 15 (43%) at 8 weeks and in 34 (97%) at 33 weeks (P < 0.0001), and median C-peptide gradually increased from 6 to 11 pmol/l (P = 0.0004) with a median change of 50% (range -50 to 3,271%) during pregnancy. GAD antibodies were present in 77% with no change from 8 to 33 weeks (P = 0.85). Multivariate regression analysis revealed a positive association between the absolute increase in C-peptide concentrations during pregnancy and decreased A1C from 8 to 33 weeks (P = 0.003).

CONCLUSIONS

A pregnancy-induced increase in C-peptide concentrations in women with long-term type 1 diabetes was demonstrated, even in women with undetectable C-peptide concentrations in early pregnancy. This increase is suggestive of improved beta-cell function and was associated with improvement in glycemic control during pregnancy.

Number of islet autoantibodies present in newly diagnosed type 1 diabetes children born to non-diabetic mothers is affected by islet autoantibodies present at birth

OBJECTIVE

Cord blood islet autoantibodies in children born to mothers with type 1 diabetes may be associated with a reduced risk of islet autoimmunity and diabetes. The aim of this study was to investigate in children with type 1 diabetes but born to non-diabetic mothers whether islet autoantibodies at birth affected their presence at diagnosis.

PATIENTS AND METHODS

Serum samples at birth and at diagnosis were available from 141 children who developed type 1 diabetes between 1 and 19 yr of age (median 9.0 yr; male/female ratio 83/58). The samples were tested for autoantibodies against glutamic acid decarboxylase, insulinoma-associated antigen 2, and insulin as well as for islet cell antibodies. The human leukocyte antigen genotype was also determined.

RESULTS

The frequency of islet autoantibodies in the umbilical cord blood was 11% compared with 91% at diagnosis. Children with fewer islet autoantibodies at diagnosis were more likely to have had autoantibodies at birth (p = 0.02). Autoantibodies present in cord blood at birth were observed in 25% (3/12) of children with no islet autoantibodies at diagnosis, in 17% (7/42) of children with one or two antibodies at diagnosis, and in only 5% (4/86) of children with more than two antibodies, demonstrating an inverse relationship between autoantibodies at birth and at diagnosis (test for trend, p < 0.001).

CONCLUSIONS

Our preliminary data suggest that exposure to cord blood islet autoantibodies may influence the presence of islet autoantibodies at the time of diagnosis of type 1 diabetes and explain why some type 1 diabetes children are islet autoantibody negative at clinical diagnosis.

Evidence for immunological priming and increased frequency of CD4+ CD25+ cord blood T cells in children born to mothers with type 1 diabetes

Maternal transmission of islet autoantibodies to children born to mothers with type 1 diabetes (T1D) has been shown to protect from autoantibodies and diabetes development later in life. However, the factors conferring disease protection are poorly understood. The aim of this study was to evaluate comparatively proinflammatory cytokines, autoantibodies and lymphocyte subsets in cord blood (CB) of children born to mothers with either T1D (n = 13), gestational diabetes (GDM) (n = 32) or healthy mothers (n = 81) in relation to transplacental passage of autoantibodies. The results are consistent with early priming of the fetal immune system only in children born to mothers with T1D. Levels of interleukin (IL)-1beta (P = 0.022), tumour necrosis factor (TNF)-alpha (P = 0.002) and IL-8 (P = 0.0012), as well as the frequency of CD4(+) CD25(+) T cells (P < 0.01) were significantly increased, and the increased levels correlated positively with anti-GAD65 autoantibody (GADA) levels. Moreover, CD4(+) CD25(+) T cells of children born to T1D mothers exhibited a more pronounced memory phenotype with increased CCR4 expression and down-regulation of CD62L. These data suggest that early activation of the fetal immune system as a consequence of maternal autoimmunity and transplacental passage of GADA may influence the generation and expansion of fetal regulatory T cells. This might induce an early antigen-specific immunological tolerance that could protect against T1D later in life.