Natural and introduced N-glycosylation sites in human IgM. (A) Domain structure of healthy human IgM with natural GL sites for N-glycosylation (N-X-S/T) indicated as red hexagons at the amino acid positions in the constant region. Introduced sites in the variable region of cases of FL are shown as green diamonds. Available oligomannoses are specifically found in the variable region as branched mannoe linked to N-acetyl glucosamines (green circles). (B) DC-SIGN is a tetramer stabilized by the neck region. It interacts with oligomannoses introduced into the antigen-binding site of FL cells via its CRDs.