Patent ID: 8241856

Claim:
A method for diagnosing rheumatoid arthritis (RA) in a human patient, the method comprising: obtaining a biological sample from the patient, providing a filaggrin peptide that has no citrulline residues (PFNC) consisting of the sequence set forth in SEQ ID NO:5, providing a citrulline-containing peptide (PFC) having the peptide sequence of said PFNC, wherein at least one arginine residue has been converted to a citrulline residue, contacting a first portion of said biological sample with said PFNC under conditions suitable for the formation of immune complexes with anti-filaggrin-autoantibodies (AFAs), contacting a second portion of said biological sample with said PFC under conditions suitable for the formation of immune complexes with AFAs, detecting and quantifying the formation of immune complexes formed between antibodies present in the sample and said PFNC and PFC, this quantification being expressed by a value X NC and X C , respectively, determining that AFAs specific to RA are present in the biological sample only if the value of X C is greater than the value of X NC , and diagnosing the patient as having RA if it is determined that AFAs specific to RA are present in the biological sample.