Anti–SS-B/La Antibodies

SARDs are a heterogeneous group of disorders characterized by dysregulation of the immune system, that starts to turn against the body’s own tissues. Major SARDs include systemic lupus erythematosus, rheumatoid arthritis, systemic sclerosis and Sjögren’s syndrome. These diseases can affect multiple organs and share common symptoms such as fatigue, fever, joint pain and skin rash. Diagnosis relies on a combination of clinical assessment and specific autoantibody tests. Early diagnosis is crucial to initiate appropriate therapy and slow down disease progression.

The SS-B/La antigen is a 48 kDa nuclear protein that binds RNA polymerase III. Anti-La/SS-B antibodies, together with anti-Ro/SSA, are conventionally associated with Sjögren’s syndrome (SjS) and with other systemic autoimmune diseases such as systemic lupus erythematosus (SLE).

Anti-SS-B/La are often detected clinically alongside anti-SS-A/Ro, and this combination is considered more diagnostically relevant. However, isolated anti-SS-B/La positivity is rare and of limited clinical value, as it may also occur in healthy individuals or in non-specific contexts.

The presence of anti-SS-A and/or anti-SS-B in asymptomatic pregnant women is associated with the risk of neonatal lupus and congenital heart block in the fetus, due to the transplacental passage of these autoantibodies. Nevertheless, the principal pathogenic role is attributed to anti-SS-A/Ro, while the contribution of anti-SS-B/La is considered secondary.

The 2016 updated ACR/EULAR classification criteria for Sjögren’s syndrome removed anti-SS-B/La as an independent diagnostic criterion, retaining only anti-SS-A/Ro owing to greater sensitivity and specificity. This change reflects evidence that isolated anti-SS-B positivity is not sufficiently specific for SjS and may be present in other autoimmune conditions.