Background/Purpose: Several studies suggested that antibodies to Domain 1 of beta2glycoprotein I (a-B2GPI-D1) represent a promising biomarker for the diagnosis and risk assessment of Antiphospholipid Syndrome (APS). This evidence comes from case-control studies with clinically defined APS patients and disease and healthy controls. This study aims to investigate the performance of a-B2GPI-D1 in a cohort of consecutive, clinically characterized samples derived from a routine diagnostic workup for the detection of antiphospholipid antibodies (aPL).
Methods: A total of 400 samples with a complete aPL panel (aCL IgG/IgM and a-B2GPI IgG/IgM by an in-house ELISA, Lupus Anticoagulant -LA- tested with a DRVVT and aPTT based method) were collected. All the samples were tested for aCL IgG/IgM, anti-B2GPI IgG/IgM, and anti-B2GPI-D1 IgG by QUANTA Flash CIA (INOVA). The clinical diagnosis/reason for aPL detection was retrieved from hospital records. The classification of APS was based on the Sapporo revised criteria. Systemic Lupus Erythematosus (SLE) was defined according to ACR criteria. Undifferentiated Connective Tissue Disease (UCTD) was classified upon international criteria.
Results: Out of 400 samples, 71 (14.5%) were positive for a-B2GPI IgG by either ELISA or CIA. Eighteen samples (4.5%) were positive for both a-B2GPI-D1 and a-B2GPI IgG by either ELISA or CIA assay, with the exception of 2 samples which were positive at low titer for a-B2GPI-D1 only (one positive also for aCL IgG CIA at low titer). These 2 sample derived from one patient with stroke and from one patient with recurrent pregnancy loss, both under investigation. Ten patients displayed a triple aPL positive profile (LA, aCL and anti-B2GPI positive at both ELISA and CIA). A significant association was found between the presence a-B2GPI-D1 (especially at medium-high titer) and triple aPL positivity (Chi Squared=195.468, p< 0.0001). Among 55 patients with positive a-B2GPI IgG (45 at low titer, 10 at medium-high titre) and negative a-B2GPI-D1 IgG, 47 (85.5%) had clinical features compatible with either APS (n=20) and/or systemic autoimmune rheumatic disease (SARD) (n=27).
|
ID code |
a-B2GPI-D1 IgG CIA (<19.9 CU) |
a-β2GPI IgG ELISA (<0.130 OD) |
a-β2GPI IgG CIA (<20 CU) |
aCL IgG ELISA (<10 GPL) |
aCL IgG CIA (<20 CU) |
LA |
Clinical features/diagnosis |
|
1-24 |
20.4 |
Neg (0.014) |
Neg (<6.4) |
Neg (2.7) |
Neg (<2.6) |
Neg |
Stroke under investigation |
|
3-04 |
22.1 |
Pos (0.52) |
Pos (40.5) |
Neg (2.3) |
Neg (7.7) |
Neg |
Reduction in visual acuity of the right eye |
|
5-16 |
23.8 |
Neg (0.041) |
Pos (44.4) |
Neg (6.7) |
Pos (25.1) |
Pos |
UCTD+obstetric APS |
|
1-71 |
24.1 |
Pos (0.748) |
Pos (262.3) |
Pos (37.5) |
Pos (85.2) |
Neg |
Obstetric Primary APS |
|
3-29 |
36 |
Neg (0.029) |
Neg (14.0) |
Neg (3.9) |
Pos (22.6) |
Neg |
Recurrent Pregnancy Loss under investigation |
|
4-35 |
37.7 |
Neg (0.090) |
Pos (21.7) |
Neg (7.3) |
Neg (11.5) |
Neg |
Fibromyalgia |
|
5-54 |
64.5 |
Pos (0.534) |
Pos (157.9) |
Pos (15.6) |
Pos (61.3) |
Pos |
SLE |
|
2-03 |
71 |
Pos (0.823) |
Pos (971.5) |
Pos (26.5) |
Pos (134.3) |
Neg |
UCTD |
|
5-35 |
71.8 |
Pos (1.564) |
Pos (1864.9) |
Pos (82.5) |
Pos (459.0) |
Pos |
UCTD |
|
2-73 |
86.7 |
Pos (1.248) |
Pos (1037.9) |
Pos (15.6) |
Pos (368.3) |
Pos |
SLE+obstetric APS |
|
3-54 |
108.9 |
Pos (1.734) |
Pos (2850.0) |
Pos (51.8) |
Pos (687.9) |
Pos |
UCTD |
|
2-31 |
114.4 |
Pos (0.341) |
Pos (369.9) |
Pos (19.4) |
Pos (85.7) |
Pos |
SLE+ vascular APS |
|
2-69 |
137.7 |
Pos (1.037) |
Pos (488.2) |
Pos (18.8) |
Pos (222.0) |
Pos |
SLE |
|
1-72 |
206 |
Pos (0.983) |
Pos (466.6) |
Pos (17.7) |
Pos (220.2) |
Pos |
Obstetric Primary APS |
|
3-06 |
285.3 |
Pos (0.997) |
Pos (614.6) |
Pos (23.7) |
Pos (193.6) |
Pos |
Vascular and Obstetric Primary APS |
|
2-64 |
419.1 |
Pos (2.231) |
Pos (8893.1) |
Pos (70.9) |
Pos (4693.6) |
Neg |
Vascular and Obstetric Primary APS |
|
4-10 |
1003.8 |
Pos (2.398) |
Pos (8647.2) |
Pos (68.1) |
Pos (1760.5) |
Pos |
UCTD with obstetric APS |
|
3-39 |
1319.2 |
Pos (2.342) |
Pos (5764.7) |
Pos (>140.0) |
Pos (1294.2) |
Pos |
SLE+Obstetric APS |
Conclusion: In a diagnostic routine setting for aPL, medium-high titer a-B2GPI-D1 were found to cluster in patients with triple aPL positivity. a-B2GPI-D1 were present mainly in patients with APS-related clinical manifestations and in patients with SARD. Nearly 80% of sample positive for a-B2GPI IgG did not display any reactivity toward D1 and the majority of these patients had a diagnosis of APS/SARD, suggesting that clinically significant a-B2GPI IgG antibodies can also be directed against other epitopes of the B2GPI molecule.
Disclosure:
L. Andreoli,
None;
A. Zanola,
None;
C. Nalli,
None;
F. Allegri,
None;
M. Mahler,
Employee of INOVA Diagnostics,
3;
G. Norman,
Employee of INOVA Diagnostics,
3;
A. Tincani,
None.
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/detection-of-anti-beta2glycoprotein-i-domain-1-antibodies-by-an-automated-chemiluminescence-assay-in-a-cohort-of-400-clinically-characterized-consecutive-routine-samples/