Measuring adrenal autoantibody response: interlaboratory concordance in the first international serum exchange for the determination of 21-hydroxylase autoantibodies.

21-hydroxylase autoantibodies (21OHAb) are the gold standard immune marker to identify patients with clinical or subclinical autoimmune Addison's disease (AAD). No assessment of interlaboratory concordance has been made for 21OHAb measurement. Serum samples from 267 patients with primary adrenal insufficiency and from 83 healthy control subjects were distributed to four independent laboratories that determined presence and titer of 21OHAb, by using radiobinding assays with either in vitro translated 35S-radiolabelled or 125I-radiolabelled autoantigen. Cohen's κ of inter-rater agreement ranged from 0.857 to 0.983, showing a very good concordance of the positive/negative score among the four laboratories. Passing-Bablok regression showed a good agreement of 21OHAb titers arranged by ranks, but important discrepancies emerged at the Bland-Altman plot, as the repeatability coefficient was much higher than the laboratory cut-offs, which indicates that results from different laboratories cannot be used interchangeably. A standardization international program for 21OHAb measurement is strongly needed.

Autoantibody responses in autoimmune ovarian insufficiency and in Addison's disease are IgG1 dominated and suggest a predominant, but not exclusive, Th1 type of response.

OBJECTIVE: Steroid-producing cell autoantibodies (SCAs) directed against 21-hydroxylase autoantibodies (21OHAbs), 17alpha-hydroxylase autoantibodies (17OHAb), and cholesterol side-chain cleavage enzyme (side-chain cleavage autoantibodies, P450sccAb) characterize autoimmune primary ovarian insufficiency (SCA-POI). The aim of the study was to analyze IgG subclass specificity of autoantibodies related to adrenal and ovarian autoimmunity. DESIGN: We studied 29 women with SCA-POI, 30 women with autoimmune Addison's disease (AAD) without POI, and 14 patients with autoimmune polyendocrine syndrome type 1 (APS1). 21OHAb isotypes were also analyzed in 14 subjects with preclinical AAD. Samples from 30 healthy women served as control group to determine the upper level of normality in the isotype assays. METHODS: Immunoradiometric assays with IgG subclass-specific secondary antibodies. RESULTS: In 21OHAb-positive sera, IgG1 isotype was detected in 90% SCA-POI and non-POI AAD sera and 67% APS1 patients. IgG1 isotype was found in 69% 17OHAb-positive SCA-POI and 100% 17OHAb-positive APS1 sera, and in 60% P450sccAb-positive SCA-POI and 80% P450sccAb-positive APS1 sera. For 21OHAb, IgG4 isotype was detected in 17% SCA-POI, 7% non-POI AAD, and 8% APS1 sera. None of the 17OHAb-positive sera was positive for IgG4. In P450sccAb-positive sera, 15% POI and 20% APS1 sera were positive for IgG4. Two 21OHAb-positive SCA-POI (7%), one 21OHAb-positive AAD (3%), three P450sccAb-positive SCA-POI (15%), and two P450sccAb-positive APS1 (20%) sera were positive for IgG4, in the absence of IgG1. All preclinical AAD sera resulted as positive for IgG1-21OHAb, but not for IgG4-21OHAb. CONCLUSIONS: The autoantibody responses in POI and AAD are IgG1 dominated, which suggests a predominant Th1 response. Selective IgG4 isotype specificity identified a small subset of patients with Th2-oriented response.