Mapping of human autoantibody epitopes on aromatic L-amino acid decarboxylase.
BACKGROUND
Aromatic l-amino acid decarboxylase (AADC) is target of autoantibodies in autoimmune polyendocrine syndrome I (APS I), especially in patients with autoimmune hepatitis. Little information is currently available on AADC autoantibody epitopes and on the interrelation between autoantibody-mediated inhibition of enzymatic activity and epitope specificity.


METHODS
We tested the immunoreactivity of full-length porcine AADC and of eight fragments of the enzyme with human serum from 18 patients with APS I, 199 with non-APS I autoimmune Addison's disease, 124 with type 1 diabetes mellitus, 36 with Graves' disease, and 141 healthy control subjects, and we evaluated the autoantibody-mediated enzymatic inhibition.


RESULTS
AADC antibodies (Ab) were detected in 12 of 18 (67%) APS I patients and in six of 199 (3%) autoimmune Addison's disease patients. Four patients with autoimmune hepatitis were all positive for AADCAb. None of the 141 healthy control subjects, 82 patients with nonautoimmune adrenal insufficiency, 124 with type 1 diabetes mellitus, and 36 with Graves' disease were found positive. Two epitope regions, corresponding to amino acids 274-299 (E1) and 380-471 (E2) were identified. Localization of E1 was confirmed by displacement studies with synthetic peptides corresponding to peptides of porcine AADC. All 12 AADCAb-positive APS I sera reacted with E1, and seven of 12 (58%) reacted also with E2. E2-specific, but not E1-specific, autoantibodies were associated with a significant inhibition of in vitro AADC enzymatic activity.


CONCLUSIONS
We mapped the human AADCAb epitopes to the middle and COOH-terminal regions of the enzyme. Autoantibodies to the COOH-terminal region induce a significant inhibition of enzymatic activity.
Candeloro
Paola
P
Department of Internal Medicine, Section of Internal Medicine and Endocrine and Metabolic Sciences, Via E. Dal Pozzo, 06126 Perugia, Italy.
Voltattorni
Carla Borri
CB
Perniola
Roberto
R
Bertoldi
Mariarita
M
Betterle
Corrado
C
Mannelli
Massimo
M
Giordano
Roberta
R
De Bellis
Annamaria
A
Tiberti
Claudio
C
Laureti
Stefano
S
Santeusanio
Fausto
F
Falorni
Alberto
A
D000293:Adolescent; D000328:Adult; D000368:Aged; D000818:Animals; D001142:Aromatic-L-Amino-Acid Decarboxylases / Q000737:chemistry* / Q000276:immunology* / Q000378:metabolism; D001323:Autoantibodies / Q000097:blood / Q000737:chemistry* / Q000378:metabolism; D001327:Autoimmune Diseases / Q000097:blood / Q000276:immunology; D001483:Base Sequence; D002648:Child; D002675:Child, Preschool; D018604:Epitope Mapping; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D008875:Middle Aged; D034421:Sus scrofa
D001323:Autoantibodies; D001142:Aromatic-L-Amino-Acid Decarboxylases