Supramolecular complexes of MHC class I, MHC class II, CD20, and tetraspan molecules (CD53, CD81, and CD82) at the surface of a B cell line JY.

The results of previous biochemical studies indicated that a fraction of MHC class II proteins is associated with four proteins of the tetraspan family, CD37, CD53, CD81, and CD82, and possibly with other membrane components, at the surface of JY B lymphoma cells. In the present communication we used a biophysical technique, namely the flow cytometric energy transfer method, to demonstrate the proximity of these molecules at the surface of the cells. Significant energy transfer (and, therefore, proximity within the 2-10 nm range) was observed between fluorescently labeled mAbs to DR, DQ, and the tetraspan molecules CD53, CD81, and CD82. Moreover, two other B cell surface molecules, CD20 and MHC class I, were found to be close to each other and to MHC class II and the tetraspan proteins, based on the observed high energy transfer efficiencies between the relevant fluorescently labeled mAbs. The character of simultaneous energy transfer from CD20, CD53, CD81, and CD82 to DR suggests that all these molecules are in a single complex with the DR molecules (or a complex of several DR molecules) rather than that each of them is separately associated with different DR molecules. Based on these data and previous biochemical results, a model is proposed predicting that the B cell membrane contains multicomponent supramolecular complexes consisting of at least two MHC class I and at least one DR, DQ, CD20, CD53, CD81, and CD82 molecules. Closer analysis of the energy transfer efficiencies makes it possible to suggest mutual orientations of the components within the complex. Participation of other molecules, not examined in this study (CD19 and CD37), in these supramolecular structures cannot be ruled out. These large assemblies of multiple B cell surface molecules may play a role in signaling through MHC molecules and in Ag presentation to T cells.