IgA1 purified from the sera of the mIgA-MIDD patient (A) and an MPCD patient (B) sera was digested partially with PNGase F for the indicated times (lanes 1–5, 7–10). Complete digestion of N-glycans was performed by incubation with PNGase F for 120 min (lanes 6, 11). Arrowheads indicate the position of PNGase F.