Reactivating the complement system using peptidic bacterial labeling tag

Abstract

The immune system plays a critical role in protecting the host against pathogens, including bacteria, viruses, and parasites. However, pathogens have evolved mechanisms to evade the immune system, for example by altering their surface proteins or by producing enzymes that can interfere with the immune response. These evasion strategies enable pathogens to escape detection and destruction by the immune system, which allows them to establish serious infections. Thus, there is a critical need for new strategies for developing antimicrobial agents. Here, we describe a novel strategy for targeting pathogens, by labeling them with a general peptide functioning as a bacterial binder, conjugated to a protein tag recognizable by the complement system, thereby activating the immune system against the target pathogen. To that end, we screened several pathogenic bacteria to find complement-resistant bacterial strain. A selected peptide binder was crosslinked with the C3b complement protein using glutaraldehyde. We show by an ELISA assay that the resulting complex binds the C5 complement protein with high affinity. We posited that by binding C5, this complex will be capable of initiating the alternative complement downstream proteolytic cascade, thereby inducing the formation of the membrane attack complex. Using this methodology, we were able to eradicate 90% of complement-resistant E. coli bacterial cells. By showing enhancement of complement sensitivity in complement-resistant pathogens, this work demonstrates the basis for new therapeutic approach capable of targeting pathogenic bacteria and activating the immune system against them.