RA serum is enriched in different anti-PAD4 antibody types. A, Serum levels of anti-PAD4 antibody isotypes and IgG subclasses from 196 RA subjects and 64 healthy controls. Comparisons were done using Student’s τ test. *** P < 0.001 and ** P < 0.01. B, Frequency of anti-PAD4 antibody isotypes and IgG subclasses in patients with RA and healthy controls. P values were obtained with Fisher’s exact test, *** P < 0.001. C, Left panel, chord diagram showing the co-occurrence of anti-PAD4 antibody isotypes in RA subjects. The different colors represent each anti-PAD4 isotype and their respective link to other isotypes. Line thickness is proportional to the Jaccard index, as shown in the matrix on the right. Right panel, Jaccard index matrix, showing the similarity between anti-PAD4 isotype pair combinations. Color intensity represents the Jaccard’s similarity coefficient, and circle size represents the −log2
P value.