In recent years, it has become clear that autoantibodies to a number of nuclear constituents have proven to be useful in the diagnosis of various connective tissue diseases. The Jo-1 autoantibody is one of a family of characteristic autoantibodies seen in myositis patients. Scientists also find them specifically in patients with myositis and associate them with a high incidence of accompanying interstitial lung disease. Doctors consider antibodies directed against the Sm marker a diagnostic criterion for SLE due to high specificity for patients with SLE. The presence of high level RNP antibodies alone are considered diagnostic of mixed connective tissue disease (MCTD) and are usually associated with a more benign disease course, while patients with low levels of RNP antibodies, together with other autoantibodies, may be observed in the serum of patients with progressive systemic sclerosis, Sjögren's Syndrome, and rheumatoid arthritis. The presence of RNP antibodies in the serum of SLE patients is usually associated with a lower incidence of renal involvement and a more benign disease course. To the contrary, patients with Sm antibodies experience a higher frequency of renal and central nervous system complications. Studies have observed autoantibodies directed against SSA and SSB in patients with SLE and Sjögren's disease. SSA antibodies are frequently present in the serum of ANA negative SLE patients, such as subacute cutaneous lupus erythematosus, a lupus-like syndrome associated with a homozygous C2 deficiency, and in a subset of patients who lack anti-dsDNA antibodies. Scl-70 antibodies are highly specific for scleroderma. Research also observes these antibodies in a minority of SLE patients. Scl-70 positive scleroderma patients tend to have a more severe disease course, more internal organ involvement, and diffuse rather than limited skin involvement. Scientists rarely find Scl-70 antibodies in other autoimmune diseases, and thus, their detection in a patient with the recent onset of Raynaud's phenomenon is highly significant. The following table summarizes the various autoantibodies noted above with respect to disease association:
The relative frequency of these autoantibodies in association with SLE and other connective tissue diseases either singularly, or as multiple autoantibodies, requires an autoantibody profile assessment of each patient's serum in order to obtain the highest degree of clinical relevance in the laboratory workup of these types of patients. Until recently, testing of autoantibodies occurred individually by indirect immunofluorescence, Ouchterlony gel diffusion, hemagglutination, radioimmunoassay, or enzyme-linked immunosorbent assay (ELISA). The exact etiology of autoimmune diseases is unknown, and the specific role played by autoantibodies in the onset of various autoimmune connective tissue diseases is obscure
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