A peptide of 8 to 20 amino acids comprising at least 8 consecutive amino acid residues having a sequence present in one of SEQ ID NOs 16, 76, 23, 77, 15, and 75. A complex of such peptide and a human recombinant MHC class II protein. Such peptide or such complex for use in the diagnosis of arthritis, preferably rheumatoid arthritis, or for the treatment of arthritis, preferably rheumatoid arthritis. A kit of parts comprising such peptide or such complex, optionally further comprising means for detecting the expression of at least one protein selected from the group consisting of CD3, CD4, Foxp3, CD25, TNF alpha, Interferon gamma, IL-17A, IL-17F, CD154, CD69, Ki 67, IL-2, IL-13 and IL-10.
