DC-SIGN fails to induce endocytosis of surface Ig by FL cells. Analysis of surface IgM internalization in response to DC-SIGN or anti-IgM treatments. Primary FL or normal B cells were treated on ice for 45 minutes with either soluble anti-IgM F(ab′)2 or DC-SIGN before incubation at 37°C to allow internalization. Flow cytometry was used to determine surface IgM expression over time in relation to zero time (100%). (A) FL samples treated with anti-IgM. (B) Normal B cells treated with soluble anti-IgM. (C) FL samples treated with soluble DC-SIGN. (D) FL cells treated with cross-linked (x) DC-SIGN. Expression of sIgM determined by FACS was analyzed using CellQuest.