Autoimmune diabetes: more than just one flavor?

Latent autoimmune diabetes in adults

CONTEXT

Autoantibodies that are reactive to islet antigens are present at the time of diagnosis in most patients with type 1 diabetes. Additionally, approximately 10% of phenotypic type 2 diabetic patients are positive for at least one of the islet autoantibodies, and this group is often referred to as "latent autoimmune diabetes in adults (LADA)." These patients share many genetic and immunological similarities with type 1 diabetes, suggesting that LADA, like type 1 diabetes, is an autoimmune disease. However, there are differences in autoantibody clustering, T cell reactivity, and genetic susceptibility and protection between type 1 diabetes and LADA, implying important differences in the underlying disease processes.

EVIDENCE ACQUISITION AND SYNTHESIS

In this clinical review, we will summarize the current understanding of LADA based on the MEDLINE search of all peer-reviewed publications (original articles and reviews) on this topic between 1974 and 2009.

CONCLUSIONS

In LADA, diabetes occurs earlier in the beta-cell-destructive process because of the greater insulin resistance. Complexities arise also because of variable definitions of LADA and type 1 diabetes in adults. As immunomodulatory therapies that slow or halt the type 1 diabetes disease process are discovered, testing these therapies in LADA will be essential.

Immunogenetics of HLA class II in Israeli patients with adult-onset Type 1 diabetes mellitus

The distribution of HLA class II alleles and genotypes in Israelis of different ethnic origin with adult-onset type 1 diabetes (T1D) was examined. The results were compared with published findings in healthy Israelis and childhood-onset T1D Israelis. An additional comparison was made between subgroups of patients with rapidly and slowly progressive adult-onset T1D (LADA). A DNA-based low-resolution analysis was performed for DRB1* and DQB1* alleles and a high-resolution analysis for DRB1*04 and DQB1*1 alleles. In all, 87% of the study group was positive for DRB1*03 or DRB1*04 compared with 36% of the healthy controls. The main alleles accounting for susceptibility to T1D were DRB1*0402, found in 77.9% of carriers of DRB1*04 and DQB1*0302, found in 74.6% of carriers of DQB1*03. The DQB1*0602 was not detected in any patient. The distribution was similar to that reported in Israeli children with T1D and significantly different from healthy Israelis. There was no significant difference in the distribution of HLA class II alleles between patients with rapidly progressive T1D or LADA. It may be concluded that the different ages of onset of T1D and its different forms of development in Israeli patients are apparently not caused by a different prevalence of HLA class II alleles.

Class III alleles at the insulin VNTR polymorphism are associated with regulatory T-cell responses to proinsulin epitopes in HLA-DR4, DQ8 individuals

A variable number of tandem repeats (VNTR) polymorphism upstream of the insulin promoter is strongly associated with type 1 diabetes. The short class I alleles are predisposing and the long class III alleles are protective. As a possible mechanism for this effect, we previously reported a two- to threefold higher insulin transcription from class III than from class I chromosomes in thymus where insulin is expressed at low levels, presumably for the purpose of self-tolerance. In this article, we confirm this finding with independent methodology and report studies testing the hypothesis that class III alleles are associated with T-cell tolerance to (pro)insulin. Cytokine release in vitro after stimulation with 21 overlapping preproinsulin epitopes was assessed in blood mononuclear cells as well as naive and memory CD4+ T-cell subsets from 33 individuals with the high-risk DRB1*04, DQ8 haplotype (12 type 1 diabetic patients, 11 healthy control subjects, and 10 autoantibody-positive subjects). No significant differences between genotypes (24 I/I subjects versus 10 I/III or III/III subjects) were observed for gamma-interferon, tumor necrosis factor-alpha, or interleukin (IL)-4. By contrast, the I/III + III/III group showed a significant threefold higher IL-10 release in memory T-cells for whole proinsulin and the immunodominant region. Given that IL-10 is a marker of regulatory function, our data are consistent with the hypothesis that higher insulin levels in the thymus promote the formation of regulatory T-cells, a proposed explanation for the protective effect of the class III alleles.

Is latent autoimmune diabetes in adults distinct from type 1 diabetes or just type 1 diabetes at an older age?

Diabetes is classified clinically into two types: type 1 and type 2 diabetes. Type 1 diabetes is an autoimmune diabetes, whereas, in contrast, type 2 diabetes is nonautoimmune. However, there is a group of phenotypic adult type 2 diabetic patients ( approximately 10%) who have islet autoantibodies similar to type 1 diabetes. These patients are said to have latent autoimmune diabetes in adults (LADA) or type 1.5 diabetes. T-cells reacting with islet proteins have been demonstrated in type 1 and type 1.5 diabetic patients. In contrast, classic autoantibody-negative type 2 diabetic patients are also negative for T-cell responses to islet proteins. Therefore, we questioned whether type 1 and type 1.5 diabetes are similar or different autoimmune diseases. We have investigated the immunological and metabolic differences between type 1, type 1.5, and classic type 2 diabetic patients. We have identified autoantibody differences, differences in islet proteins recognized by T-cells, and differences in insulin resistance. We have also identified a small group of patients who have T-cells responsive to islet proteins but who are autoantibody negative. These patients appear to be similar to type 1.5 patients in having decreased stimulated C-peptide values. These immunological differences between type 1 and type 1.5 diabetes suggest at least partially distinct disease processes.