Defense mechanisms in insects: certain integumental proteins and tyrosinase are responsible for nonself-recognition and immobilization of Escherichia coli in the cuticle of developing Ceratitis capitata.

A defense mechanism in the cuticle of developing C. capitata was demonstrated using an in vitro system consisting of isolated cuticular tyrosinase from C. capitata, cuticular tyrosinase-free proteins, tyrosine, and E. coli. The simultaneous presence of the above components resulted in the formation of large immobilized E. coli aggregates. By contrast, omission of any of the above components failed to produce such aggregates. In other words, E. coli retained their mobility and viability. The results indicate that certain cuticular proteins are responsible for the nonself-recognition, since they are able to bind to the E. coli surface in vitro, and a reactive tyrosine derivative is generated by the action of cuticular tyrosinase for the immobilization and probably killing of E. coli. Based on these studies the most likely explanation for the nonself-recognition and immobilization and/or killing of bacteria is the production of E. coli-protein complexes and their crosslinking through quinone intermediate.