Mapping the dextran sulfate binding site on CD2

This study has analysed the binding of a series of anti-CD2 monoclonal antibodies (MoAbs) to T cells in the presence of the sulfated polysaccharide dextran sulfate (2.3 sulfates/monosaccharide, 500 kDa) (DXS) to define the DXS binding site on CD2. The results show that DXS interacts primarily at the T11(2) epitope. Thus five anti-CD2 MoAbs which bound to the T11(2) epitope were inhibited in their binding by DXS. In contrast, seven anti-CD2 MoAbs that totally inhibited sheep red blood cells (SRBC) rosetting (identifying the T11(1) epitope) were unaffected in their binding to T cells in the presence of DXS. Three MoAbs which partially inhibited SRBC rosetting and thereby defining only part of the T11(1) epitope, were also inhibited in their binding by DXS. Consistent with the conclusion that the DXS binding site on CD2 is associated with the T11(2) epitope was the observation that interaction of DXS with CD2 resulted in augmented binding of the four MoAbs defining the T11(3) epitope, possibly reflecting an increased expression of the T11(3) (activation, CD2R) epitope of CD2. Collectively, the data presented support the notion that a natural ligand for the T11(2) epitope of CD2 will be identified as a sulphated carbohydrate structure.