Analysis of immunoreactivity of sera from systemic sclerosis patients and healthy controls of Caucasian origin. ELISA assays with the recombinant amino-terminal (rF16 (a)) and carboxy-terminal (rF6H (b)) halves of human fibrillin-1 are shown. Microtiter plates were coated with purified rF16 and rF6H or bovine serum albumin. The plates were incubated with test sera diluted 1:100 for 2 hours at room temperature. After incubation with horseradish peroxidase-conjugated secondary antibody and color development, the absorbance was determined by an ELISA reader. Positive binding was defined as more than 2 SD above the mean (dashed line) of the control sera. If the blank value exceeded the sample value the absorbance was set to zero in the figure. None of the sera showed a positive reactivity to rF16 or rF6H.