Peripheral blood biomarkers of cell-specific autoimmunity. Studies in children at increased risk for type 1 diabetes.

Summary, in English

Objective

While the incidence of children suffering
from autoimmune type 1 diabetes (T1D) is increasing in Sweden and worldwide,
the underlying etiology and cellular mechanisms behind this remain unknown. The
predisposition of the high-risk HLA DR-DQ genotype and as yet unknown
environmental triggers lead to autoimmunity and the onset of T1D, which is
preceded by islet beta-cell autoantibodies acting as markers for ongoing
autoimmunity. This study aims to identify peripheral blood biomarkers to
predict and explain cellular autoimmune processes leading to beta-cell loss
before and after seroconversion. We also investigate whether immune tolerance
treatment with GAD-alum affects T-cells in nondiabetic children at increased
genetic risk of T1D prospectively followed in longitudinal studies.

Methods

Children participating in the Swedish TEDDY
cohort with or without islet beta-cell autoantibodies were studied. Complete
blood count in these children was analyzed and related to autoantibody status,
gender, HLA genotype, and glucose metabolism measures. HbA1c, a predictive
biomarker for a subsequent autoantibody or T1D, was analyzed in the TEDDY
cohort from Finland, Germany, Sweden, and the US. HbA1c trajectories were also
studied in the progression from developing a single autoantibody to diagnosing
T1D. Children aged 4–17.99 years at enrollment participating in the DiAPREV-IT2
clinical trial were studied and different T-cells were immunophenotyped to
investigate the immune tolerance treatment with GAD-alum.

Results

A reduction in neutrophil counts primarily
in boys and children with the HLA-DR3-DQ2/DR4-DQ8 genotype, and a reduction of
red blood cell counts, hemoglobin, and hematocrit primarily in girls and in
children with HLA-DR3-DQ2/DR4-DQ8 were inversely associated with autoimmunity
and the number of beta-cell autoantibodies. A reduction in red blood cell
indices (MCH and MCV) was associated with increased HbA1c, by increased number
of beta-cell autoantibodies. Reduction in red blood cell count, hemoglobin, and
hematocrit levels were associated with increased fasting blood glucose.
Increased red blood cell counts and hemoglobin, hematocrit, and MCH were
associated with increased fasting insulin. Increased HbA1c was associated with
an increased risk of T1D regardless of the number and type of autoantibodies.
The development of IA-2A as a second or fourth autoantibody was associated with
decreased HbA1c levels. The HbA1c trajectories presented a more rapid increase
of HbA1c as the number of autoantibodies increased from one to three.
GAD-alum-treated children had lower T-helper cell (CD3+ CD4+ T-cells ) and
cytotoxic T-cell (CD3+ CD8+ T-cells) levels 18–24 months after two
immunizations with GAD-alum.

Conclusion

Reductions in neutrophil levels, red blood
cells, and red blood cell parameters and increased levels of HbA1c are all
associated with multiple autoantibodies, reflecting a prominent islet
autoimmune burden. The reduction in different complete blood counts with
increasing numbers of beta-cell autoantibodies may suggest an unknown effect of
impaired beta-cell function on hematopoiesis. Predicted trajectories of HbA1c
could be used to further develop a model to predict the time to T1D diagnosis
in children with multiple autoantibodies. The decrease in HbA1c associated with
the appearance of IA-2A may be a consequence of aggressive autoimmune
destruction of beta-cells leading to insulin leakage into the bloodstream.
These results should prove helpful for understanding the pathogenesis of T1D
and better predicting the onset of T1D in seroconverted children. Immunization
with GAD-alum has a long-term effect on T-cells 18–24 months after treatment.