SSB/La Ab in serum
Etiology
- Sjogren's Syndrome-sicca complex (60%)
- systemic lupus erythematosus (SLE) (15%)
Reference interval
- Normal: Negative
Principle
Highly purified SSB antigen is bound to microwells & stabilized for extended shelf life. Diluted patient sera are placed in the microwells & incubated. If anti-SSB antibodies are present, they will bind to the antigen in the microwell. The microwells are then washed to remove residual sample & a second incubation with anti-human IgG conjugated to alkaline phosphatase is carried out. The conjugate will bind immunologically to the anti-SSB IgG antigen-antibody complex, forming a 'sandwich' consisting of:
Conjugate (Enzyme-labeled Anti-human IgG)
Unbound conjugate is removed in the subsequent washing step. Enzyme substrate is then added to the microwell & if bound conjugate is present, the colorless substrate (p-nitrophenyl phosphate), will be hydrolyzed to form a yellow end product, (p-nitrophenol). The reaction is then stopped and the color fixed. The intensity of the color is measured photometrically at 405 nm & is proportional to the concentration of anti-SSB present in the patient sample.
Clinical significance
- associated with Sicca symptoms[4]
- associated with photosensitivity
- associated with neonatal lupus[4]
SSB antibodies,(identical to the previously described La antibody), are found in approximately 15% of patients with systemic lupus erythematosus (SLE). They are primarily considered a serological marker for Sjogren's Syndrome-sicca complex & are detected in approximately 60% of such patients. As with anti-SSA (Ro) antibody, anti-SSB (La) is frequently detected in precipitin assays in sera yielding false-negative ANA by immunofluorescence techniques.
Anti-SSB invariably occurs in sera containing anti-SSA antibodies and virtually all anti-SSB-positive sera contains anti-SSA. There appear to be important differences that distinguish SLE patients who produce only anti-SSA from those producing both anti-SSA & SSB. There is a great similarity in nonrenal findings in these two groups, but there is a striking difference in the frequency and severity of renal disease. SLE patients producing both SSA and SSB antibodies have a much lower incidence of nephritis than those patients producing anti-SSA alone. Since the presence of anti-SSB antibodies, therefore, is associated more frequently with a milder form of autoimmune disease their detection would aid in the diagnosis & therapy of rheumatic disease.
Neonatal lupus with cogenital heart block effects ~2% of children with mothers having anti-SSA or anti-SSB, regardless if mother has SLE or Sjogren's syndrome.[4]
Specimen
Serum is separated from the clot & refrigerated, 2-8 degrees C for short term storage or stored frozen, -20 degrees C, for long term storage. Avoid freeze-thaw cycles. CAUTION: Serum samples should not be heat inactivated, as this may cause false positive results.
Interpretation
- <20 EU/mL: Negative for antibodies to SSB
- 20-25 EU/mL: Equivocal for antibodies to SSB
- >25 EU/mL: Positive for antibodies to SSB
More general terms
More specific terms
Additional terms
- Lupus La protein; Sjoegren syndrome type B antigen; SS-B; La ribonucleoprotein; La autoantigen (SSB)
- SSA/Ro Ab in serum
Component of
References
- ↑ Henry, John Bernard, Clinical Diagnosis amd Management by Laboratory Methods, W. B. Saunders Co., Philadelphia, 1991. pp 891-892.
- ↑ The Physicians Guide to Anti-DNA Antibody Testing, Diamedix Corporation, Miami, Aug. 1989. pp 1-6.
- ↑ Summary of Procedure. DiaMedix Corporation, Miami, June 1991. pp 1-8.
- ↑ 4.0 4.1 4.2 4.3 Medical Knowledge Self Assessment Program (MKSAP) 17, American College of Physicians, Philadelphia 2015