Antibodies to extracted nuclear antigens in the blood

Normally, the concentrations of antibodies to extracted nuclear antigens RNP / Sm, Sm, SS-A (Ro), SS-B (La) - less than 20 IU / ml, 20-25 IU / ml - boundary values; to the antigen Scl-70 antibodies are normally absent.

This study consists in the quantitative determination of IgG-AT against extractable nuclear antigens - RNP / Sm, Sm, SS-A (Ro) and SS-B (La) in serum. Antibodies to extracted nuclear antigens (ENA) are complexes of soluble ribonucleoproteins. Antibodies against various nuclear antigens are an important diagnostic feature for monitoring and diagnosing various rheumatic diseases.

• Antibodies to RNP / Sm antigens (AT to the protein components of U ₁ - small nuclear ribonucleoprotein - U ₁ RNA) are detected with mixed connective tissue disease, less often with systemic lupus erythematosus and other rheumatic diseases. The concentration of antibodies does not correlate with the activity and development of exacerbation. In patients with systemic lupus erythematosus, in the serum of which antibodies to Sm-Ar are present, antibodies to the ribonucleoprotein are not detected. To avoid false positive results, an immunoblot analysis is used.
• Sm-Ar consists of five small nuclear RNAs (U ₁, U ₂, U ₄, U ₅, U ₆ ) associated with 11 or more polypeptides (A ', B ^' / B ^', C, D, E, F , G). Antibodies to the Sm antigen are specific for systemic lupus erythematosus and are present in 30-40% of patients with this disease. These antibodies are very rare in other connective tissue diseases (in the latter case, their detection indicates a combination of diseases). The concentration of antibodies to the Sm antigen does not correlate with the activity and clinical subtypes of systemic lupus erythematosus. Antibody to the Sm antigen is one of the criteria for diagnosing systemic lupus erythematosus.

The frequency of detection of antibodies to various extractable nuclear antigens

Type АТ	Diseases	Frequency,%
Sm	Systemic lupus erythematosus	10-40
PNP	Systemic lupus erythematosus	20-30
	Mixed connective tissue diseases	95-100
SS-A (Ro)	Systemic lupus erythematosus	15-33
	Systemic scleroderma	60
	Neonatal lupus erythematosus	100
	Sjogren's Syndrome	40-70
SS-B (La)	Systemic lupus erythematosus	10-15
	Systemic scleroderma	25
	Sjogren's Syndrome	15-60
Scl-70	Systemic scleroderma	20-40

• SS-A (Ro) - polypeptides forming complexes with Ro RNA (hY1, hY3 and hY5). AT to Arg SS-A (Ro) are most often found in Sjogren's syndrome / disease and systemic lupus erythematosus. In systemic lupus erythematosus, the production of these antibodies is associated with a certain set of clinical manifestations and laboratory disorders: photosensitivity, Sjogren's syndrome, hyperproduction of rheumatoid factor. The presence of these antibodies in the blood of pregnant women increases the risk of developing neonatal lupus-like syndrome in newborns. AT to Arg SS-A (Ro) can be increased in 10% of patients with rheumatoid arthritis.
• SS-B (La) -Ag - nucleocytoplasmic phosphoprotein complex with Ro small nuclear RNA (Ro hY1-hY5), transcriptor of RNA polymerase III. АТ to Ar SS-B (La) is found in diseases and Sjogren's syndrome (40-94%). In systemic lupus erythematosus, antibodies to SS-B (La) are more often detected at the onset of a disease that develops in the elderly (9-35%) and is associated with a low incidence of nephritis.
• Scl-70-Ar-topoisomerase I is a protein with a molecular weight of 100,000 and its fragment has a molecular weight of 67,000. The AT to Scl-70 is more often detected in diffuse (40%), less often with limited (20%) form of systemic scleroderma. They are highly specific for this disease (sensitivity 20-55% depending on the analytical method) and are a poor prognostic sign. The presence of Scl-70 antibodies in systemic scleroderma in combination with the carriage of HLA-DR3 / DRw52 genes increases the risk of pulmonary fibrosis 17-fold. The detection of Scl-70 antibodies in the blood in patients with an isolated Raynaud phenomenon indicates a high probability of systemic scleroderma.

[1], [2], [3], [4], [5], [6]