Molecular computer graphic of an antibody-antigen complex. At top is the antigen. The green region is the antigenic determinant, or epitope: the part of the antigen recognised by the antibody. At bottom is the antibody produced in response to the presence of the antigen. The green area here is the antibody combining site, which recognises & binds with the epitope. The small yellow & white areas are charged residues within the antibody combining site which are believed to be involved in the interaction. The antigen shown is hen egg white lysozyme, which was injected into a mouse to produce a mouse antibody. Space-filled computer graphic. Photographed by MM 23/7/88.