Immune responses to insulin in patients with insulin-dependent diabetes mellitus

Kinetics of the post-onset decline in zinc transporter 8 autoantibodies in type 1 diabetic human subjects

CONTEXT

Zinc transporter 8 (ZnT8) is a newly discovered islet autoantigen in human type 1A diabetes (T1D).

OBJECTIVE

The objective was to document changes in ZnT8 autoantibody (ZnT8A) titer and prevalence after onset of disease in relationship to 65 kDa glutamate decarboxylase antibody (GADA) and islet cell antigen antibody (IA2A).

DESIGN/PATIENTS

Autoantibody radioimmunoprecipitation assays were performed on sera from three groups: 21 individuals monitored every 3 months from diagnosis for 2.5 yr; 61 individuals monitored at six monthly intervals for 5-12 yr; and a cross-sectional study of 424 patients with T1D of 20-57 yr duration. Circulating C-peptide was determined as an index of residual β-cell function.

RESULTS

ZnT8A titers declined exponentially from clinical onset of T1D with a t(1/2) ranging from 26 to 530 wk, similar to C-peptide (23-300 wk). Life-table analysis of antibody prevalence to 12 yr indicated that ZnT8A measured with either Arg325 or Trp325 probes persisted for a shorter interval than IA2A. Although prevalence of ZnT8A, IA2A, and GADA were comparable at disease onset (70.4 vs. 73.4 vs. 64%), only 6.7% of individuals remained ZnT8A positive after 25 yr compared with 19.5% for IA2A and 25.9% for GADA. Titers of ZnT8A and IA2A in seropositive individuals decreased progressively, whereas GADA remained elevated consistent with periodic reactivation of GADA humoral autoimmunity.

CONCLUSIONS

ZnT8 humoral autoreactivity declines rapidly in the first years after disease onset and is less persistent than IA2A or GADA in the longer term. ZnT8A determination may be a useful measure of therapeutic efficacy in the context of immune-based clinical interventions.

Immune responses to insulin and lymphocyte subclasses at diagnosis of insulin-dependent diabetes and one year later

Insulin induced proliferation of blood mononuclear cells, numbers of blood B and T cells, of blood lymphocytes bearing interleukin 2 receptors or HLA class II molecules were assayed at diagnosis and one year later in children with insulin-dependent diabetes mellitus (IDDM) and in healthy children. Insulin and islet cell antibodies were also studied. The numbers of lymphocytes expressing HLA class II molecules and NK cells were increased at diagnosis. T cells of the helper/inducer (CD4+) phenotype and interleukin 2 receptor positive lymphocytes were increased both at diagnosis and one year later. At diagnosis, insulin induced proliferation of blood mononuclear cells in 65% and one year later in 50% of the patients. Insulin antibodies were detected in 10% and islet cell antibodies in 90% of patients at diagnosis, and in 67% and 78%, respectively, one year later.