Diagnostic performance and validation of autoantibody testing in myositis by a commercial line blot assay.
OBJECTIVE
Serological testing for myositis-specific or associated autoantibodies [myositis-specific antibody (MSA) and myositis-associated antibody (MAA)] is useful for the diagnosis of idiopathic inflammatory myopathies (IIMs). However, available assays are neither standardized nor validated. The objective is to evaluate the accuracy of a commercial line blot assay for myositis diagnosis.


METHODS
IgG antibodies against Jo-1, PL-7, PL-12, PM/Scl, Ku, Mi-2 and Ro52 antigens were detected by a line blot and in-house RNA immunoprecipitation or immunoblot. We tested sera from 208 IIM patients, 50 healthy subjects and 180 control patients (11 non-autoimmune myopathy, 23 muscular dystrophy, 11 UCTD, 68 SLE, 36 SSc, 22 SS and 9 arthropathy).


RESULTS
MSAs or MAAs were detected in 98 (47%) out of the 208 IIM patients by line blot: anti-Jo-1 in 43 (21%), anti-PL-7 or anti-PL-12 in 8 (4%), anti-Mi-2 in 9 (4%), anti-PM/Scl in 9 (4%), anti-Ku in 10 (5%) and anti-Ro52 in 49 (24%). Overall specificity was: 100% for anti-Jo-1, anti-PL-7 or PL-12 and anti-PM/Scl; 96% for anti-Ku; 98% for anti-Mi-2; and 76% for anti-Ro52. In-house testing confirmed line blot results regarding anti-Jo-1, anti-PM/Scl and anti-Ku, while it was more accurate than line blot in detecting anti-Mi-2 (7 vs 4% sensitivity, 100 vs 98% specificity), and anti-aminoacyl-tRNA synthetase (anti-ARS) non-Jo-1 antibodies (11 vs 4% sensitivity, 97 vs 99% specificity).


CONCLUSIONS
Line blot could be a suitable serological test in the diagnostic workup for myositis, and it represents a reliable alternative to more time-consuming procedures. Continuous effort is recommended in order to improve its accuracy.
Ghirardello
Anna
A
Department of Clinical and Experimental Medicine, Division of Rheumatology, University of Padova, Via Giustiniani 2, 35128 Padova, Italy.
Rampudda
Mariaelisa
M
Ekholm
Louise
L
Bassi
Nicola
N
Tarricone
Elena
E
Zampieri
Sandra
S
Zen
Margherita
M
Vattemi
Gaetano A
GA
Lundberg
Ingrid E
IE
Doria
Andrea
A
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001323:Autoantibodies / Q000276:immunology; D016022:Case-Control Studies; D002648:Child; D005260:Female; D006801:Humans; D015151:Immunoblotting / Q000379:methods* / Q000592:standards; D007558:Italy; D008297:Male; D008875:Middle Aged; D009220:Myositis / Q000276:immunology* / Q000378:metabolism; D011237:Predictive Value of Tests; D011933:Reagent Kits, Diagnostic; D012680:Sensitivity and Specificity; D012698:Serologic Tests / Q000379:methods / Q000592:standards; D013223:Statistics as Topic; D013548:Sweden; D055815:Young Adult
D001323:Autoantibodies; D011933:Reagent Kits, Diagnostic