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-EC869 (the C-terminal 289 residue CT fragment). Does not inhibit toxic activity of CdiA from other toxin-immunity modules or strains of E.coli. Interacts with the C-terminal fragment (CT) of cognate toxin protein CdiA-EC869.