Table 1.
Histone peptides used in this study.
Fig 1.
Reactivity with histone peptides containing apoptosis-associated modifications and their unmodified counterparts.
Plasma samples from SLE patients were tested in ELISA with the indicated modified histone peptides and their unmodified counterparts (i.e. H4p, H2Bp, and H3p). Patients with rheumatoid arthritis (RA) or systemic sclerosis (SSc), and healthy individuals were used as controls. * p<0.01 compared to the unmodified equivalent as determined using the Mann-Whitney U test; # p<0.01 compared to healthy subjects and patients with other autoimmune diseases and ^ p<0.01 compared to patients with other autoimmune diseases using the one-way ANOVA test. H4p, histone H4 peptide; H4pac, histone H4 peptide acetylated at lysine 8, 12 and 16; H2Bp, histone H2B peptide; H2Bpac, histone H2B peptide acetylated at lysine 12; H3p, histone H3 peptide; H3pme, histone H3 peptide trimethylated at lysine 27.
Fig 2.
Reactivity with histone peptides containing apoptosis-associated modifications and with their unmodified counterparts in SLE patients with and without lupus nephritis.
(A) Plasma samples from SLE patients with or without nephritis were tested in ELISA with the indicated modified histone peptides and their unmodified counterparts (i.e. H4p, H2Bp, and H3p). (B) Ratio of the reactivity with the respective modified histone peptide divided by the reactivity with the unmodified counterpart, for SLE patients with and without nephritis. In all cases the one-way ANOVA test was used for statistical comparison. * p<0.001. H4p, histone H4 peptide; H4pac, histone H4 peptide acetylated at lysine 8, 12 and 16; H2Bp, histone H2B peptide; H2Bpac, histone H2B peptide acetylated at lysine 12; H3p, histone H3 peptide; H3pme, histone H3 peptide trimethylated at lysine 27.
Table 2.
Specificity and sensitivity of (modified) histone peptide ELISAs in SLE patients.
Fig 3.
H4pac appears superior in distinguishing SLE patients from healthy and disease controls.
ROC curves for (modified) histone peptide ELISAs were calculated for SLE vs. all controls (A), SLE vs. healthy controls (B), SLE vs. disease controls (C), lupus nephritis vs. all controls (not including SLE without nephritis) (D), and lupus nephritis vs. all controls including SLE without nephritis (E). *, p<0.05 vs. unmodified; #, p<0.01 vs. H2Bpac; ^, p<0.01 vs. H3pme.
Table 3.
Correlation coefficients between reactivity with modified and unmodified histone peptides, and other serological assays in patients with lupus nephritis.
Table 4.
Correlation coefficients between reactivity with modified and unmodified histone peptides, dsDNA, chromatin or histones, and disease activity (SLEDAI) or complement C3 levels in SLE patients with lupus nephritis.
Fig 4.
Reactivity with (multiple) modified peptides is associated with increased SLEDAI and follow disease activity during disease flares.
(A) SLE patients with nephritis were sorted into groups depending on the number of different modified histone peptides they show reactivity with, and the mean SLEDAI and C3 levels were compared between these groups. (B) Examples of reactivity with H4pac and H4p along with the SLEDAI score and anti-dsDNA reactivity in 4 patients that experienced a disease flare after initial treatment. Patient characteristics are detailed in S1 Table. H4p, histone H4 peptide; H4pac, histone H4 peptide acetylated at lysine 8, 12 and 16; H2Bp, histone H2B peptide; H2Bpac, histone H2B peptide acetylated at lysine 12; H3p, histone H3 peptide; H3pme, histone H3 peptide trimethylated at lysine 27