Models to explain the improved lytic activity of the monovalent^Cys444 dimer (MD).

(A) Representation of the different cross-linked antigen lattices that might be formed on the cell surface by wild-type bivalent and dimerized monovalent antibody. MAC indicates membrane attack complex. (B) Probable differences in the relative rotational freedom of the Fc regions of the bivalent and monovalent antibody dimers, when bound to CD3 antigen on a cell surface.