The target antigen against SS-B (La) is an accessory protein of RNA polymerase III (48 x 103). The molecular biological properties of the La protein have been elucidated. The transcription unit of RNA polymerase also includes small hY-RNAs of the ribonucleic acid particle component, which is also recognized by anti-SS-A (Ro). Therefore, at least for the time being, the Ro protein and the La protein are the same components in the cell, or a part of the same component of the ribonucleic acid protein particles. This may be the reason why even if Ro and La do not have the same sequence that may cross-react, they can still be detected simultaneously in the patient's serum.

Basic Information

Specialist classification: growth and development check classification: immunological examination

Applicable gender: whether men and women apply fasting: not fasting

Analysis results:

Below normal:

Normal value:

Above normal:

Normal people are negative.

A positive indication may have SLE.

Tips: The results obtained by enzyme immunoassay are occasionally false positives. Normal value

Normal people are negative.

Clinical significance

The clinical significance of anti-SS-B (La) is similar to that of anti-SS-A (Ro), but its clinical sensitivity is low.

(1) 40% to 90% of patients with primary Sjogren's syndrome.

(2) 9% to 35% of patients with SLE.

(3) About 75% of patients with congenital heart disease and neonatal lupus.

On the other hand, the clinical specificity of the above diseases is high. Accordingly, anti-SS-B (La) is often negative even in patients with anti-SS-A (Ro)-positive rheumatoid arthritis. However, it has been reported that anti-SS-B (La) can be detected in patients with rheumatoid arthritis without using animal-derived antigens. Compared with anti-SS-A positive/anti-SS-B negative patients, anti-SS-A and anti-SS-B positive SLE patients have less kidney damage and less anti-dsDNA, and this antibody pattern is often late. Seen in patients with sexual SLE.


In the IFT assay of Hep-2 as matrix, anti-SS-B (La) is a nuclear fine particle type, usually high titer, and negative staining in the middle stage of division. ANA negative serum, anti-SS-B (La) is usually negative. In addition, anti-SS-B (La)-positive serum is usually positive for SS-A (Ro), so it is only meaningful to detect anti-SS-B when it is positive for SS-A. If the results are negative for ANA and anti-SS-A, and anti-SS-B (LA) positive, this is often suspicious, especially when:

(1) The results obtained by enzyme immunoassay are occasionally false positive.

(2) A positive band was observed only at 48×103 in immunoblotting.

Inspection process

The methods used include:

(1) Precipitation method (immune double diffusion, reverse phase immunoelectrophoresis), commonly used thymus extract as a substrate.

(2) Immunoblotting, three bands appear at 48 x 103.

(3) ELISA, commonly used for affinity purification or recombinant antigen.

Not suitable for the crowd

There are no taboos.

Adverse reactions and risks

There are no related complications and hazards.