The crystal structures of complexes formed between lysozyme and antibody fragments.

Type c lysozymes, and hen egg lysozyme in particular, have been extensively used to study the immune response because of their strong immunogenicity, the availability of many natural variants to study cross-reactivity, and the possibility to correlate these results with the known three-dimensional structure of lysozymes from several species. To date, the structure of six different murine monoclonal anti-lysozyme antibodies has been studied as a complex between the Fab fragment and antigen. In some cases, the structure of the uncomplexed Fab is also available, giving detail at the atomic level of the changes which take place during the formation of the antibody-antigen complex. The bacterially-expressed Fv molecule, the simplest fragment of an immunoglobulin retaining an intact antigen-binding site, has been studied for three of the monoclonal anti-lysozyme antibodies. Recombinant Fv fragments have opened up the possibility of using site-directed mutagenesis to study the effect of amino acid changes at the antibody-antigen interface. The six monoclonal antibodies appear to recognize epitopes which are localised on three different regions of the lysozyme surface.