The Dependence of Immunological Cross-Reactivity upon Sequence Resemblance among Lysozymes

Precipitin techniques were used for cross-reactivity studies with rabbit antisera to seven different bird egg white lysozymes. A similar study was previously made with the same antisera by the micro-complement fixation technique. There is an excellent correlation between cross-reactivity measured by micro-complement fixation and that measured by the quantitative precipitin technique. However, the latter technique is less economical of materials and less able to discriminate between closely related lysozymes. Although cross-reactivity measured by immunodiffusion, a qualitative precipitin technique, is correlated with that measured by the above two techniques, it is far less sensitive to small antigenic differences. The above correlations permitted a review of the dependence of immunological cross-reactivity upon amino acid sequence resemblance for several other proteins besides lysozyme. Even though the published data are fragmentary compared with those available for lysozyme, it seems to be a general rule that native proteins differing by more than 30 to 40% in sequence fail to cross-react in direct precipitin or complement fixation tests.