Anti-U1snRNP antibodies typically appear in both SLE and MCTD. In MCTD, the presence of U1 snRNP is required for diagnosis. MCTD is typified by the high-titer RNP antibody activity in isolation; anti-RNP antibody activity in SLE commonly accompanies anti-Sm antibodies. U2 snRNP autoantibodies are myositis-associated autoantibodies and are found frequently, but not exclusively, in patients with myositis. Other myositis-associated autoantibodies include autoantibodies to U1-RNP, U2-RNP, PM/SCL and Ku.Antibodies to Mi-2 occur in 15-20% of patients with adult dermatomyositis. Ku antibodies have been found in 10% of patients with polymyositis/scleroderma overlap syndrome and in 10% of systemic lupus erythematosus patients. Patients with polymyositis/scleroderma overlap who are positive for Ku antibodies usually have a mild disease with a good prognosis.
The presence of SRP antibodies is predominantly associated with polymyositis. The prevalence of SRP antibodies in idiopathic inflammatory myopathy is 4-5%.
Antibodies against PL-7 and PL-12 have a prevalence of approximately 3% to up to 6% in myositis patients, partly overlapping with SLE, SSc or interstitial lung fibrosis. The prevalence of antibodies against EJ and OJ in myositis patients is up to 3%.
R0-52 is observed in approximately 30% of patients with myositis.
PM-Scl antibodies are associated with a high frequency of myositis-scleroderma overlap.
Anti-155/140 antibodies are directed against the transcription intermediate family-1 (TIF-1) members TIF-1α, and TIF-1γ. –TIF-1α/γ antibodies are frequently detected is juvenile dermatomyositis (DM) and may present a more severe clinical course. The frequency of anti–TIF-1α/γ antibodies in juvenile DM is 23–29%. These antibodies are frequently detected in patients with cancer-associated DM. The incidence of cancer in anti–TIF-1α/γ–positive patients with adult DM is 42–75%.
Anti-clinically amyopathic dermatomyositis (CADM)/P140/MDA5 autoantibodies are specifically detected in Japanese patients with dermatomyositis and are known to have a strong association with rapidly progressive interstitial lung disease (RP-ILD). Japanese studies have shown that anti-MDA5 is seen in between 38%-50 of juvenile dermatomyositis (JDM patients), all of whom had ILD. A small subsets of with very high titers of antiMDA5 had RP-ILD. The reported rates of ILD in USA patients with JDM are far lower than in adult DM.
Anti-NXP-2/MJ antibodies associated with young onset DM, calcinosis, no internal organ involvement and good response of myopathy to therapy. Anti-NXP-2/MJ reported in juvenile DM is also found in adult PM/DM, and could be a new useful biomarker. Studies show that anti-NXP-2 and anti-TIF-1γ antibodies are frequent DM specificities (found in 55% of patients) and are present in most patients with cancer-associated DM.
Anti-SAE may occur in patients who present with clinically amyopathic dermatomyositis first and then progress to develop myositis with a high frequency of systemic features including dysphagia but a low frequency of interstitial pneumonia. Anti-SAE positive patients had mainly skin and muscle manifestations while dysphagia, interstitial lung disease, arthritis and constitutional symptoms were absent.
Sporadic inclusion body myositis (sIBM) is an inflammatory myopathy characterized by both degenerative and autoimmune features. Circulating autoantibody against a 43 kDa muscle autoantigen has been demonstrated in sIBM. Anti-cN1A autoantibodies were shown to be over 70% sensitive and over 95% specific for sIBM.
Autoantibodies to five of the aminoacyl-transfer RNA (tRNA) synthetases have been described, and each is associated with a syndrome of inflammatory myopathy with interstitial lung disease (ILD) and arthritis. Anti-KS was more closely associated with ILD than with myositis.
The presence of anti–U3 RNP autoantibodies in systemic sclerosis(SSc)identifies a well-defined clinical subset of the disease. This antibody should be considered in African American and/or male SSc patients who have positive ANA with pure nucleolar staining. SSc patients with anti–U3 RNP are younger and have more rapid progression of disease. Patients with anti–U3 RNP have a significantly greater frequency of internal organ involvement, skeletal muscle involvement and pulmonary hypertension.