IGHA1 and autoimmune disease: In this regard, asCD had a higher relative abundance of the TPL cluster (data not shown)compared to HC and UC, this could indicate that the ratio IgA1/IgA2is decreased in CD, and that the difference in ratio could be associatedwith autoimmune diseases.23 This couldbe further investigated by quantitative assays, such as isotype-specificELISAs or by adding isotopically labeled standards to the samplesfor MS analysis.