Comparison of anti-human insulin antibodies detection by commercial enzyme-linked immunosorbent assay kit, displacement enzyme-linked immunosorbent assay and radioimmunoassay, in Thai diabetic patients

ATP4A autoimmunity in pediatric patients with type 1 diabetes and its relationship to blood count, iron metabolism, and vitamin B12

OBJECTIVE

We aimed to assess the prevalence of autoantibodies against the 4A subunit of the gastric proton pump (ATP4A) in pediatric type 1 diabetes (T1D) patients and explore the relationship between ATP4A positivity and blood cell count, iron turnover, and vitamin B12 concentration.

SUBJECTS

The study included 94 (59% female) T1D children (aged 12.5 ± 4.1 years, T1D duration 4.2 ± 3.6 years, HbA1c 7.3 ± 1.5% (57 ± 12.6 mmol/mol) with no other autoimmune diseases.

METHODS

ATP4A antibodies were measured in T1D patients using a radioimmunoprecipitation assay. Blood cell count, iron concentration, total iron binding capacity, ferritin, transferrin, hepcidin, and vitamin B12 concentration were measured in all the study participants.

RESULTS

A total of 16 (17%) children were ATP4A positive. Serum concentrations of ferritin were significantly lower in ATP4A positive than in antibody negative subjects (P = .034). Overall the levels of ATP4A antibodies (ATP4A Index) correlated positively with the age at T1D diagnosis (r = 0.228, P = .026) and negatively with ferritin levels (r = -0.215, P = .037). In ATP4A positive patients, the ATP4A Index correlated positively with age at diagnosis (r = 0.544, P = .032) and negatively with vitamin B12 levels (r = -0.685, P = .004).

CONCLUSIONS

ATP4A antibodies were present in a significant proportion of children with T1D. Higher ATP4A levels in T1D children are associated with lower, yet still fitting within the normal range, levels of vitamin B12, and ferritin. Routine screening of T1D children for gastric autoimmunity (ATP4A) should be considered with follow-up of those positive for vitamin B12 and iron deficiency.

Anti-parietal cell antibodies - diagnostic significance

Anti-parietal cell antibodies (APCA) are an advantageous tool for screening for autoimmune atrophic gastritis (AAG) and pernicious anemia (PA). The target for APCA is the H+/K+ ATP-ase. It has been demonstrated, that APCA target both, the alpha, and beta subunits of the proton pump, although the major antigen is the alpha subunit. Circulating serum APCA can be detected by means of immunofluorescence, enzyme-linked immunosorbent assay - currently the most commonly used method, and radioimmunoprecipitation assay (RIA) - the 4A subunit has been optimized as a molecular-specific antigen probe. RIA is the most accurate method of antibody assessment, characterized by highest sensitivity. APCA can be found in 85-90% of patients with PA. Their presence is not sufficient for diagnosis, because they are not specific for PA as they are also found in the circulation of individuals with other diseases. APCA are more prevalent in the serum of patients with T1D, autoimmune thyroid diseases, vitiligo, celiac disease. People with autoimmune diseases should be closely screened for AAG/PA. The anemia develops longitudinally over many years in APCA-positive patients, symptomless, slowly promotes atrophy of the gastric mucosa and parietal cells. APCA are present in 7.8-19.5% of the general healthy adult population. A fraction of these sero-positive people, will never develop AAG or PA. An interesting and not fully explained question is whether APCA presence is related to Helicobacter pylori infection. APCA are found in up to 20.7% of these patients. H. pylori is implicated as one of the candidates causing AAG.

Immunogenicity of human and bovine insulin in type 1 diabetes mellitus patients

BACKGROUND

The advantages of synthetic insulin (human insulin) over bovine insulin in the treatment of type 1 diabetes mellitus (DM) are much debated in terms of potency and purity. Immunogenicity is one of several factors that determine potency and safety. This study was designed to investigate and study the difference in immunogenicity of human and bovine insulin. We investigated anti-insulin antibody (AIAB) status in 69 type 1 DM patients receiving insulin therapy. Group 1 had 33 patients treated with bovine insulin, and group 2 had 32 patients treated with human insulin. All patients had received their respective insulin therapy for a minimum period of 1 year and had no history of change in insulin type. Forty-three subjects from the normal population were the control group.

METHODS

AIABs were assayed in serum samples of all subjects using a semiquantitative radioimmunoassay kit. The Kruskal-Wallis non-parametric and Mann-Whitney U tests were used to study the difference in immunogenicity of human and bovine insulins.

RESULTS

The Kruskal-Wallis test showed that antibody titers in the three groups significantly differed (P<0.001). The Mann-Whitney U test showed no significant difference in AIAB titer between the treatment groups. AIAB titers in the two treatment groups differed significantly from that of the control group, independently (P<0.001). High titers of AIABs are present in patients receiving bovine and human insulin compared to that of the normal population.

CONCLUSIONS

Bovine and human insulins are antigenic, and there is no significant difference in AIAB titer. Prospective studies are required to determine the long-term clinical significance of these antibodies.

Cell-mediated immune responses to GAD and beta-casein in type 1 diabetes mellitus in Thailand

We measured the cell-mediated immune response to GAD and bovine beta-casein in 38 type 1 and 37 type 2 diabetic patients who visited diabetic clinics or who were hospitalized in Bangkok, Thailand, and in 43 normal controls, by using a lymphoproliferation assay. Positive results against GAD were found in 29/38 (76.3%) type 1, 6/37 (16.2%) type 2 diabetic patients and 1/43 (2.3%) normal controls. Positive results against bovine beta-casein were found in 18/38 (47.4%), 5/37 (13.5%) and 1/43 (2.3%) of these subjects, respectively. The frequencies of the positive results and the magnitude of the responses to both antigens in type 1 diabetic patients were significantly higher than those in the other two groups (P<0.001). In addition, the prevalence of a positive lymphoproliferative response to these antigens in type 1 diabetic patients was higher than that of anti-GAD antibody positivity in the same group of subjects (26.3%). Thus, the prevalence of positive lymphoproliferative response to GAD in type 1 diabetic patients studied was higher than the prevalence of other autoimmune markers previously reported in type 1 diabetic patients in Thailand.