KRT13 and rheumatoid arthritis: However, we found no significant difference between the levels of Cit-CK13, a major citrullinated peptide that we identified in the saliva samples, in patients with RA and healthy controls Therefore, it is highly probable that the human salivary citrullinated peptide detected by Tar et al. was Cit-CK13, although we did not perform the dot blot analysis ourselves.