Based on the primary structure of the CFFCHP1 peptide, the antigen that detected a significantly higher percentage of RA-ILD for the IgA isotype (anti-CFFCHP1-IgA 59.4% in RA-ILD, Table 2), a novel peptide antigen incorporating acetyl-lysine within the peptide sequence was synthesized. This evidence concerns the gene CD79A and rheumatoid arthritis.