CD1d favors MHC neighborhood, GM1 ganglioside proximity and low detergent sensitive membrane regions on the surface of B lymphocytes.

Cluster of differentiation 1 (CD1) represents a family of proteins which is involved in lipid-based antigen presentation. Primarily, antigen presenting cells, like B cells, express CD1 proteins. Here, we examined the cell-surface distribution of CD1d, a subtype of CD1 receptors, on B lymphocytes. Fluorescence labeling methods, including fluorescence resonance energy transfer (FRET),were employed to investigate plasma membrane features of CD1d receptors. High FRET efficiency was observed between CD1d and MHC I heavy chain (MHC I-HC), β2-microglobulin(β2m) and MHC II proteins in the plasma membrane. In addition, overexpression of CD1d reduced the expression of MHC II and increased the expression of MHC I-HC and β2m proteins on the cell-surface. Surprisingly, β2m dependent CD1d isoform constituted only ~15% of the total membrane CD1d proteins. Treatment of B cells with methyl-β-cyclodextrin (MβCD) / simvastatin caused protein rearrangement; however, FRET demonstrated only minimal effect of these chemicals on the association between CD1d and GM1 ganglioside on cell-surface.Likewise, a modest effect was only observed in a co-culture assay between MβCD/simvastatin treated C1R–CD1d cells and invariant natural killer T cells on measuring secreted cytokines (IFNγ and IL4). Furthermore,CD1d rich regions were highly sensitive to low concentration of Triton X-100. Physical proximity between CD1d, MHC and GM1 molecules was also detected in the plasma membrane. An intricate relationship between CD1d, MHC, and lipid species was found on the membrane of human B cells. Organization of CD1d on the plasma membrane might be critical for its biological functions.