Anti-ETA IgG neutralizes the effects of Pseudomonas aeruginosa exotoxin A

Background. The opportunistic pathogen Pseudomonas aeruginosa causes severe infections in immunocompromised hosts. Among P. aeruginosa-infected burn patients, mortality may reach as high as 50%. Due to their immunocompromised status, burn patients may benefit from passive immunotherapy against infection. As a potential multivalent immunoglobulin therapy, specific polyclonal antibodies against four P. aeruginosa virulence factors, including exotoxin A (ETA), were prepared. Materials and methods and results. In this study, we analyzed the ability of ETA antibody (ETA-Ab) to neutralize the in vivo effects of ETA. Adult mice injected with purified ETA suffered 100%, mortality. The cytosolic DNA of their hepatocytes was fragmented, indicating ETA induction of apoptosis. In addition, multiprobe RNase protection assays showed that ETA upregulates the expression of the genes for proinflammatory cytokines as well as apoptosis genes in the livers of ETA-injected mice. Treatment with ETA-Ab prior to ETA injection prevented mortality, ETA-induced hepatocyte DNA fragmentation, and upregulation of the cytokine and apoptosis-related genes. The role of ETA during P. aeruginosa infection of the burn wound was examined by determining the in vivo virulence of P. aeruginosa PA103 and its isogenic, ETA-deficient mutant PA103Omega::toxA using the thermally injured mouse model. The lethality, local spread, and systemic spread of PA103Omega::toxA were significantly reduced compared to PA103. Conclusion. These results suggest that (1) ETA induces apoptosis in hepatocytes, (2) specific cytokines are produced in response to ETA, (3) ETA-Ab neutralizes these effects, and (4) ETA contributes to the spread of A aeruginosa during burn wound infection. (C) 2002 Elsevier Science (USA).