IGHA1 and systemic lupus erythematosus: Interestingly, observing the absolute amounts of each antibody subclass, and although IgA2 is clearly elevated in both groups of patients, it becomes evident that the most dramatic increase is in the IgA1 fraction that displays a mean value below 2 μg/mL in healthy controls and close to 10 μg/mL in active SLE patients.