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 (PubMed:21829394). Neutralizes the toxic activity of cognate toxin CdiA-o11-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 (PubMed:21829394, PubMed:26305955) (Probable). Expression of this locus confers protection against other bacteria carrying the locus. Interacts with the C-terminal fragment (CT, residues 88-377) of cognate toxin protein CdiA-o11-EC869 (PubMed:21829394, PubMed:23236156, PubMed:26449640). Probably recognizes only the toxic DNase subdomain of CdiA-o11-EC869 (approximately residues 222-377) (Probable). The sequences characterized in (PubMed:21829394) and crystallized in (PubMed:23236156) are actually derived from cdiA-CTo11/cdiIo11, an orphan cdiA-CT/cdiI module that only encodes the cdiA CT fragment and its associated cdiI. It is however identical to that shown in this entry, which does have the elements necessary for gene expression.