Preferential pairing of T-B specificities in the same antigen: the concept of directional help.

It is important for an effective planning of the new generation of vaccines to consider that the eventual response is regulated by the interplay of stimulating and suppressing epitopes, resulting in dominance of certain sites over others, and that in order for a molecule to be crossimmunogenic with the outside invader both B and T epitopes must be present. However, T-B cooperation is not random but is guided by preferential pairing of sites within a single macromolecule; this situation can be explained by antigen processing by B cells and paratope mediated interference with endosomial degradation.