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Original Studies |
Department of Internal Medicine and Endocrine and Metabolic Sciences (S.L., F.C., F.S., A.F.), University of Perugia, 06126 Perugia, Italy; Institute of Endocrinology (A.D.B., V.I.M., A.Be.) and Department of Clinical and Experimental Medicine "F. Magrassi" (A.Bi.), 2nd University of Naples, 80131 Naples, Italy; and Department of Molecular and Clinical Endocrinology and Oncology (R.R.), University "Federico II", 80131 Naples, Italy.
Address all correspondence and requests for reprints to: Alberto Falorni, M.D., Ph.D., Department of Internal Medicine and Endocrine and Metabolic Sciences, University of Perugia, Via E. Dal Pozzo, 06126 Perugia, Italy. E-mail: falorni{at}dimisem.med.unipg.it
| Abstract |
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| Introduction |
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The identification of subjects with an ongoing adrenal autoimmune process is important in the clinical management of patients with endocrine autoimmune diseases often associated with adrenal insufficiency, such as Hashimotos thyroiditis, Graves disease, or insulin-dependent diabetes mellitus (IDDM). In patients with endocrine autoimmune diseases, the presence of ACA has been used to estimate the risk for clinical adrenal insufficiency (18, 19, 20, 21, 22, 23, 24). Several studies have shown, however, that an adrenal autoimmune process does not lead necessarily to clinical Addisons disease. Thus, remission of subclinical adrenocortical dysfunction may occur in ACA-positive subjects (22, 25). Furthermore, it has recently been reported that the presence of ACA and 21OHAb is a marker of rapid progression toward clinical adrenal insufficiency in children (23), but only of low progression in adult subjects with endocrine autoimmune diseases (24).
It is still unknown whether production of adrenal autoantibodies is the result of an autoantigen-driven mechanism or the mere consequence of the destruction of target cells. It is also unclear whether the levels of adrenal autoantibodies correlate with the degree of adrenal dysfunction in the preclinical period.
In the present study, we followed up the serum levels of 21OHAb and ACA in a group of initially ACA-positive subjects without clinical signs of adrenal insufficiency. Autoantibody data were correlated with the degree of preclinical adrenal insufficiency, as estimated by the analysis of biochemical parameters of adrenal function.
| Materials and Methods |
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Studying a large group of 3,020 patients with 1 or more
endocrine autoimmune diseases, a total of 26 (0.9%) ACA-positive
subjects was identified. Of these ACA-positive subjects, 3 Graves
patients with ophtalmopathy were not included in the follow-up study
because a corticosteroid treatment was started either before (n =
2) or during (n = 1) our follow-up study. Furthermore, follow-up
samples from an additional 4 ACA-positive subjects were not available.
Hence, 19 ACA-positive subjects [male/female (M/F) ratio: 5/14, median
age: 31 yr, range: 1844 yr] entered the follow-up study (Fig. 1
). Most of the ACA-positive subjects had
been longitudinally studied and described in a previous paper (22). Of
the 19 subjects studied, 8 (42%) presented with autoimmune
thyroiditis, 5 (26%) with premature ovarian failure (POF), 4 (21%)
with Graves disease, 3 (16%) with IDDM, 2 (10%) with atrophic
gastritis, 2 (10%) with vitiligo, and 1 (5%) with diabetes insipidus
(Table 1
). The patient with diabetes
insipidus (no. 11) was positive for arginine vasopressin cell
autoantibodies (26, 27).
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ACA assay
ACA were determined using an indirect immunofluorescence method on cryostatic sections of monkey adrenal gland (22). Levels of ACA were expressed as end-point dilution titer.
21OHAb assay
21OHAb were determined in coded samples using a radiobinding assay that uses in vitro translated recombinant human 35S-21OH and protein A-Sepharose (Pharmacia, Biotech, Uppsala, Sweden) (11). 21OHAb levels were expressed as a relative index (21OHAb index) using one positive and two negative standard sera, which were included in each assay (11). The upper level of normal of the 21OHAb index was estimated as the mean + 3 SD of the results obtained when analyzing sera from 200 healthy subjects (mean + SD: 0.027 ± 0.011, range: -0.02 to 0.059) and was 0.06. The samples with a 21OHAb index more than 0.7 were titrated using 1:100 to 1:500 dilutions.
Adrenocortical functional studies
The adrenocortical function of the 19 ACA-positive subjects was evaluated by measuring basal plasma levels of ACTH, cortisol, aldosterone, and plasma renin activity (PRA), as previously described (22). Cortisol plasma levels were also evaluated 60 min after an iv infusion of 0.25 mg synthetic ACTH (normal peak response, > 20 µg/dL = 552 nmol/L).
According to previously reported criteria (21, 22) and based on the
results of the biochemical analyses, five stages of adrenocortical
dysfunction were recognized in subjects with adrenal autoantibodies:
stage 0 = normal adrenal function; stage 1 = high PRA and
normal/low aldosterone levels; stage 2 = along with
impaired cortisol response to ACTH; stage 3 = along with increased
basal ACTH levels; stage 4 = clinically overt Addisons disease.
Normal subjects (stage N) were those with normal adrenal function and
absence of adrenal autoantibodies. The 19 ACA-positive subjects were
subdivided into 3 groups (Table 1
): group A (n = 8 subjects; M/F
ratio = 4/4) who developed clinical Addisons disease at
follow-up; group B (n = 6 subjects; M/F ratio = 1/5) with
deterioration of adrenal function throughout the study, but without
development of clinical Addisons disease; and group C (n = 5
subjects; M/F ratio = 0/5) with remission of adrenal dysfunction
after a 24 yr follow-up period.
Statistical analysis
Differences in levels of 21OHAb or ACA titer, in relation to stage of preclinical adrenal dysfunction, were tested by ANOVA with Bonferronis correction for multiple comparisons after logarithmic transformation of antibody levels. In some analyses, samples of stage 2 and stage 3 were considered as a single group (stage 2+3) because both stages identify a subclinical dysfunction of the ACTH-cortisol axis, as compared with stage 1, which is characterized by the exclusive dysfunction of the aldosterone-renin axis. The correlation between 21OHAb levels and ACA titers was evaluated by Spearmans rank correlation test. Linear regression between antibody titers and stages of adrenal dysfunction was evaluated after logarithmic transformation of the 21OHAb index and ACA titers. Differences in the serum levels of adrenal autoantibodies between the beginning and the end of the study were evaluated by the nonparametric Wilcoxon test for paired samples. In all tests, a P value less than 0.05 was considered significant.
| Results |
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The presence of 21OHAb was demonstrated in two subjects from group B,
23 yr before the first demonstration of the presence of ACA (Table 2
).
After logarithmic transformation, the levels of 21OHAb and ACA were
significantly and positively associated with the severity of adrenal
dysfunction (ANOVA, P < 0.0001 for both 21OHAb and
ACA; linear regression: r = 0.549, P < 0.0001 and
r = 0.745, P < 0.0001 for 21OHAb and ACA titers,
respectively) (Fig. 2
). The 21OHAb index
of samples of stage 0 was significantly lower than that of samples of
stage 2 (corrected P < 0.05), stage 3 (corrected
P < 0.01), and stage 4 (clinical Addisons disease;
corrected P < 0.001). The 21OHAb index of samples of
stage 4 was also significantly higher than that of samples of stage 1
(corrected P < 0.01). In addition, when samples of
stages 2 and 3 were considered as a single group (stage 2+3), the
21OHAb index of stage 0 and 1 was also lower than stage 2+3 (corrected
P < 0.001 and P < 0.05). No
statistical difference in the 21OHAb index was observed between stage 2
and stage 3 or between stage 3 and stage 4 or between stage 2 and stage
4.
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Comparison of samples at entry and at the end of the follow-up period
showed a significant increase in 21OHAb index (P =
0.041) and ACA titer (P = 0.002) in those subjects with
progression of adrenal dysfunction (groups A and B) (Table 2
).
The remission of biochemical signs of adrenal dysfunction was associated with the disappearance of both ACA and 21OHAb in five subjects (nos. 1519).
| Discussion |
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Our study confirms previous reports (18, 23, 24) that showed that 21OH is a major autoantigen recognized by ACA during the preclinical period. In addition, we show that: 1) levels of adrenal autoantibodies correlate with the severity of adrenal dysfunction in the preclinical period; and 2) early biochemical signs of adrenal dysfunction may spontaneously remit, in parallel to the disappearance of both ACA and 21OHAb.
The observation that all our 19 ACA-positive subjects, as well as all
the follow-up samples of 14 subjects with progressive adrenal
dysfunction, were positive for 21OHAb supports the hypothesis that 21OH
is the major adrenal autoantigen recognized by autoantibodies. A
similar finding has recently been reported by Betterle et
al. (24) on a group of 48 ACA-positive individuals. In our study,
21OHAb appeared before ACA in two subjects with progressive adrenal
dysfunction (Table 2
). Thus, the presence of 21OHAb may be a sensitive
marker of an ongoing adrenal autoimmune process in patients with
endocrine autoimmune diseases. In a recent study of IDDM patients (18),
it was proposed that 21OHAb can be used as a marker for the large-scale
screening of patients with endocrine autoimmune diseases for adrenal
insufficiency. However, as also demonstrated by previous studies (22, 24, 25), the presence of adrenal autoantibodies does not lead
necessarily to clinical Addisons disease.
In a previous study (22), the disappearance of ACA was associated with the spontaneous remission of early subclinical adrenal dysfunction. An important finding of our present study is the demonstration that the disappearance of circulating 21OHAb can parallel that of ACA in subjects with spontaneous remission of early subclinical adrenal dysfunction. Thus, our study demonstrates unequivocally that a spontaneous remission of early stages of subclinical adrenal dysfunction can occur and is associated with the disappearance of adrenal autoantibodies.
Although it has previously been shown that the risk for clinical Addisons disease is increased in subjects with ACA and 21OHAb, especially in the presence of the susceptible HLA-DR3 haplotype and of complement-fixing ACA (24), little information is currently available on the relationship between adrenal autoantibody levels and the severity of preclinical adrenal insufficiency. In our study, a clear correlation between levels of ACA/21OHAb and the degree of the adrenal dysfunction was observed in 19 subjects with preclinical adrenal insufficiency. Accordingly, levels of 21OHAb and ACA are a useful marker to monitor the progression of the adrenal autoimmune process and may be useful to improve our understanding of the mechanisms responsible for autoantibody production.
21OHAb production may be a secondary, side-effect of the T-cell-mediated destruction of adrenocortical cells with the subsequent release of 21OH or 21OH-related peptides. However, we observed a significant increase in 21OHAb index between stage 1 and stage 2+3, but not between stage 0 and 1 or between stages 2, 3, and 4. The absence of a significant change in 21OHAb levels in the advanced stages of adrenal dysfunction supports the hypothesis that 21OHAb production is not exclusively dependent on the release of an intracellular autoantigen. Furthermore, the observation that disease-related 21OHAb epitopes seem to be conserved among different patients and restricted to the central and COOH-terminal regions of the autoantigen (30, 31) can be interpreted to indicate that 21OHAb are the result of a selective, oligoclonal, and epitope-specific process that generates autoantibodies at increasing affinity for the antigen.
A significant increase in 21OHAb levels may be the sign of a switch from an early, potentially reversible activation of the immune system to a destructive and irreversible phase of the autoimmune process. Based on the results of our study, the switch toward a progressively destructive autoimmune process is likely to be associated with the stage 23 of adrenal dysfunction. In fact, in all the subjects who were at stage 2 or 3 at entry, adrenal dysfunction progressed during the follow-up. On the other hand, remission of adrenal dysfunction was observed in 50% subjects who were at stage 01 at entry.
In conclusion, the results of our study demonstrate that levels of adrenal autoantibodies correlate with the degree of the adrenal dysfunction in subjects with preclinical adrenal insufficiency, and they suggest that production of high levels of adrenal autoantibodies is strictly associated with the activation of the destructive phase of the autoimmune disease process.
| Footnotes |
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Received March 5, 1998.
Revised May 22, 1998.
Accepted June 17, 1998.
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