Equilibrium binding of cytotoxic T lymphocytes to class I antigen

Cloned cytotoxic T lymphocytes specifically bind to purified alloantigen that has been immobilized on a surface. When the time course was examined, it was found that binding reached a plateau level within about 1 h at 37 degrees C, at which time about 30% of the CTL were tightly adhered to the surface. Analysis of the properties of binding demonstrated that this does not simply result because only a fraction of the cells in the clonal population are capable of binding. Instead, the binding is shown to result from an equilibrium involving tightly bound and unbound (or weakly bound) cells. Thus, the cells cycle between a tightly bound and unbound state, despite continuous contact with the Ag-bearing surface. The results suggest that dissociation of the bound cells may be an actively signaled event. A model that could account for these results based on activated CD8 binding is discussed.