Serologic cross-reactivity of T11 target structure and lymphocyte function-associated antigen 3. Evidence for structural homology of the sheep and human ligands of CD2.

T11 target structure (T11TS) and lymphocyte function-associated antigen (LFA) 3 are the cell-surface glycoproteins on sheep and human erythrocytes (E) binding to cluster differentiation 2 (the E-receptor) on T cells in E rosette formation. Here we show that this functional cross-reactivity is most likely due to a structural homology of these molecules. A rabbit antiserum to sheep T11TS is shown to cross-react with LFA-3 in several independent assays: (a) rabbit anti-T11TS antiserum blocks the formation of E rosettes by human T cells with both autologous and xenogeneic (sheep) E by binding to the respective E; (b) the antiserum blocks the binding of anti-LFA-3 monoclonal antibody to human E; and (c) it reacts with purified LFA-3 in Western blotting. Together, these findings demonstrate that T11TS on sheep E and LFA-3 on human E are serologically related, providing further support for the notion that T11TS and LFA-3 are the sheep and human forms of the same cell interaction molecule.