Immunity protein component of a toxin-immunity protein module, which functions as a cellular contact-dependent growth inhibition (CDI) system. CDI modules allow bacteria to communicate with and inhibit the growth of closely related neighboring bacteria in a contact-dependent fashion. Neutralizes the toxic activity of cognate toxin CdiA-YPIII (residues 954-1077). Does not inhibit toxic activity of CdiA from other toxin-immunity modules. Interacts with the C-terminal DNase fragment (residues 954-1077) of cognate toxin CdiA-YPIII. Encoded in a defective cdi locus that has been inactivated by gene rearragements and deletions.