Core fucosylation of serum IgM. Immunoblots of serum samples of the LAD II patient taken before (0 days) and at 6 different time points during fucose therapy (as indicated) and from a healthy control (control). Samples were analyzed with the mouse MoAb CAB4 that recognizes Fuc-1,6-GlcNAcβ in the core of N-linked glycans. First antibody was detected by binding with a secondary antibody that did not cross-react with human Igs. The same serum samples were analyzed for the amount of IgM protein present by ELISA using antihuman IgM antibodies as described in Materials and Methods. Serum IgM levels were quantitated by regression analysis from the reactivity of purified human IgM. Amounts given on the left refer to the amounts that were loaded on the immunoblot gel.