Fig. 2

Correlation analysis. Reactivity of serum samples from Dutch patients with sporadic inclusion body myositis was measured by anti-cN-1A IgG ELISA (Euroimmun) based on recombinant full-length cN-1A, by ELISAs based on three synthetic peptides representing major cN-1A epitopes (n = 51), and by immunoprecipitation (IP) of in vitro translated full-length cN-1A (n = 30). Results by anti-cN-1A IgG ELISA were plotted against a the maximum OD450 values measured by either of the three peptide ELISAs and b against the efficiency of immunoprecipitation. Dotted lines represent cutoff values (anti-cN-1A IgG ELISA, ratio ≥1.0; IP high efficiency, >5% of input; IP low efficiency, >1% of input). In panel a, triangles/circles depict serum specimens with a maximum OD450 value below/above the cutoff value of the respective peptide ELISA (peptide 1, OD450 ≥ 0.384; peptide 2, OD450 ≥ 0.270; peptide 3, OD450 ≥ 0.280). Correlation was evaluated by Pearson’s correlation coefficients (r) as indicated. P values <0.05 were considered significant