SSB and systemic lupus erythematosus: Using hierarchical clustering and principal component analysis, it was possible to classify four subgroups of SLE individuals associated with four corresponding clusters of functionally linked autoantigens: SLE 1a: original SLE autoantigens Ro60, La, and Sm complex; SLE1b: proteins involved in RNA, DNA and chromatin processing; SLE2: receptor-regulated SMAD (main signal transducers for receptors of the TGF-β superfamily); and SLE3: toll-like receptor pathways and lymphocyte development.