Background/Purpose: The significance of a low titer of SSA and/or SSB antibodies (SSA/B-Ab) in individuals with clinical or other laboratory findings suggestive of Sjögren’s syndrome (SS) is unclear. Low titers may represent false positive immunoassay results, seropositivity in the absence of clinical disease, or true markers of a connective tissue disease, such as SS. It is unclear whether low titers represent a distinct phenotype or one more similar to those with negative titers. We sought to explore the association between SSA/B titer levels and phenotypic features of SS, including histopathological characteristics.
Methods: The Sjögren’s International Collaborative Clinical Alliance (SICCA) is an NIH-funded registry of individuals with suspected or established SS. Each participant undergoes a uniform and protocol-driven evaluation for SS, including rheumatologic, oral, and ophthalmologic examinations, serologic testing, labial salivary gland biopsy, and ocular staining. SSA/B-Ab testing was performed by Quest Laboratories, using an automated multiplex flow immunoassay. Positive results were expressed in “antibody index” (AI) units and provided as continuous variables measure up to a level of 8 AI. Levels more than >8 AI were not quantified. We compared the mean and prevalence of phenotypic features of SS by category of SSA/B-Ab (High: both SSA-Ab and/or SSB-Ab>8; Low: SSA-Ab and/or SSB-Ab≥1 but both ≤8; Negative: both SSA-Ab and SSB-Ab<1).
Results: Among the SICCA participants, low titers of SSA/B-Ab were present in 277 (14.1%), high titer SSA/B-Ab in 434 (22.1%) and negative SSA/B-Ab in 1256 (63.8%). The associations between these three strata of SSA/B-Ab titers and phenotypic features of SS are shown in the Table. Mean age decreased while focus score increased as SSA/B-Ab titers increased. The percentage of participants with each phenotypic feature was greater for those with high SSA/B-Ab compared with those with low titers and greater for those with low titers compared with negative titers.
|
Table: Phenotypic Features of Sjogren’s Syndrome by SSA/B Antibody Titer |
|||||||
|
|
High |
Low |
Negative |
p |
|||
|
|
N |
Mean or % |
N |
Mean or % |
N |
Mean or % |
|
|
Age (years) |
454 |
50.79 |
287 |
51.33 |
1270 |
54.48 |
<.0001 |
|
Focus score (foci/4 mm2) |
367 |
3.32 |
204 |
2.79 |
527 |
1.50 |
<.0001 |
|
ANA≥1:320 |
455 |
69.5% |
287 |
44.3% |
1276 |
16.1% |
<.0001 |
|
Rheumatoid factor ≥ 30 IU/ml |
454 |
49.8% |
287 |
34.2% |
1275 |
10.0% |
<.0001 |
|
IgG>1445 mg/dl |
455 |
62.0% |
285 |
49.5% |
1273 |
12.1% |
<.0001 |
|
C4<16 mg/dl |
455 |
22.6% |
285 |
17.2% |
1273 |
10.6% |
<.0001 |
|
WBC ≤ 4000/mm3 |
448 |
27.5% |
283 |
19.4% |
1266 |
7.4% |
<.0001 |
|
FLS or F/SLS focus score ≥ 1* |
434 |
74.0% |
277 |
57.4% |
1256 |
19.1% |
<.0001 |
|
Germinal centers in lip biopsy |
454 |
23.8% |
285 |
7.4% |
1273 |
4.2% |
<.0001 |
|
Schirmer’s ≤5 mm either eye |
454 |
46.0% |
286 |
37.8% |
1276 |
24.3% |
<.0001 |
|
Ocular surface staining ≥ 3 |
454 |
94.1% |
286 |
83.2% |
1275 |
67.2% |
<.0001 |
|
Unstimulated saliva ≤0.5 ml/5 min |
455 |
64.4% |
286 |
61.2% |
1274 |
48.0% |
<.0001 |
|
*FLS=focal lymphocytic sialadenitis; F/SLS=focal /sclerosing lymphocytic sialadenitis |
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Conclusion: There is a higher prevalence of all phenotypic features of SS among those with higher SSA/B-Ab titer. Low antibody titers occur in approximately 14% of patients suspected of having SS and may represent an intermediary phenotype distinct from those with high or negative titers.
Disclosure:
M. McAdams DeMarco,
None;
M. Y. Lam,
None;
S. Shiboski,
None;
L. A. Criswell,
None;
C. Shiboski,
None;
A. N. Baer,
None.
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