Displays only Anti-ssDNA activity when tested by ELISA. Undiluted antibody shows a strong Scl-70 precipitin band. Specificity verified by a precipitin line of identity with the CDC-AF reference serum and by ELISA procedures using both native DNA and ssDNA. Does not cross-react at a dilution of 1:100 when tested against purified Ro/SS-A, La/SS-B, Sm, Scl-70, nRNP, dsDNA, or Jo-1 antigens in an ELISA system designed to detect IgG antibody.