Antibodies to extracted nuclear antigens in blood

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

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

• Antibodies to RNP/Sm antigens (AB to protein components of U ₁ - small nuclear ribonucleoprotein - U ₁ RNA) are detected in mixed connective tissue disease, less often in 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 whose blood serum antibodies to Sm-Ag are present, antibodies to ribonucleoprotein are not detected. Immunoblotting analysis is used to exclude false positive results.
• Sm-Ag 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 very rarely appear 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. Antibodies to the Sm antigen are one of the diagnostic criteria for systemic lupus erythematosus.

Frequency of detection of antibodies to various extractable nuclear antigens

Type AT	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 that form complexes with Ro RNA (hY1, hY3 and hY5). AB to Ag SS-A(Ro) are most often detected 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 abnormalities: 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. AB to Ag SS-A(Ro) can be elevated in 10% of patients with rheumatoid arthritis.
• SS-B(La)-Ag is a nucleocytoplasmic phosphoprotein complex with Ro small nuclear RNA (Ro hY1-hY5), a transcriptor of RNA polymerase III. AT to Ag SS-B(La) are detected in Sjögren's disease and syndrome (in 40-94%). In systemic lupus erythematosus, antibodies to SS-B(La) are more often detected at the onset of the disease, developing in old age (in 9-35%) and associated with a low incidence of nephritis.
• Scl-70-Ag - topoisomerase I - a protein with a molecular weight of 100,000 and its fragment with a molecular weight of 67,000. AT to Scl-70 are more often detected in diffuse (40%), less often in 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 carriage of the HLA-DR3/DRw52 genes increases the risk of developing pulmonary fibrosis by 17 times. Detection of Scl-70 antibodies in the blood of patients with isolated Raynaud's phenomenon indicates a high probability of developing systemic scleroderma.

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