The effects of rabbit-derived polyclonal Ab against PcrV, a protein involved in the translocation of type III secreted toxins of Pseudomonas aeruginosa, was investigated in two animal models of P. aeruginosa sepsis. In a mouse survival study, the i.v. administration of anti-PcrV IgG after the airspace instillation of a lethal dose of P. aeruginosa resulted in the complete survival of the animals. In a rabbit model of septic shock associated with Pseudomonas-induced lung injury, animals treated with anti-PcrV IgG intratracheally or i.v. had significant decreases in lung injury, bacteremia, and plasma TNF-α and significant improvement in the hemodynamic parameters associated with shock compared with animals treated in a similar manner with nonspecific control IgG. The administration of anti-PcrV F(ab′)2 showed protective effects comparable to those of whole anti-PcrV IgG. These results document that the therapeutic administration of anti-PcrV IgG blocks the type III secretion system-mediated virulence of P. aeruginosa and prevents septic shock and death, and that these protective effects are largely Fc independent. We conclude that Ab therapy neutralizing the type III secretion system has significant potential against lethal P. aeruginosa infections.

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The association of O-antigen serotypes with type III secretory toxins was analyzed in 99 clinical isolates of Pseudomonas aeruginosa. Isolates secreting ExoU were frequently serotyped as O11, but none were serotype O1. Most of the isolates that were nontypeable for O antigen did not secrete type III secretory toxins.Lung infections caused by Pseudomonas aeruginosa are frequently associated with a high rate of mortality, particularly in immunocompromised patients (1,4). In addition to an increase in the prevalence of drug-resistant organisms, these poor outcomes of P. aeruginosa pneumonia appear to be due to the development of acute lung injury and septic shock (1,3,4,28). Among the various virulence factors of P. aeruginosa, lung injury and sepsis in infected hosts depend largely on the expression of exoenzyme S and its coregulated toxins secreted by the type III secretion system (TTSS) (10,15,29,30,34). The TTSS, which delivers toxins directly into the cytosol of cells, is utilized by most pathogenic gram-negative bacteria (11,14).The TTSS, including secretion, translocation, and regulation apparatuses, is encoded by the exoenzyme S regulon in P. aeruginosa (10, 33). However, the genes for the type III secretory toxins (TTS toxins) are distributed in various regions of the P. aeruginosa chromosomal DNA separate from the exoenzyme S regulon (8, 26). To date, four TTS toxins have been identified in P. aeruginosa (10,33). ExoS (exoenzyme S) and ExoT (exoenzyme T), having ADP-ribosyltransferase activities, diminish macrophage motility and phagocytosis (12) and are associated with mortality in animal models (2,(20)(21)(22). ExoY possesses adenylate cyclase activity and affects cell morphology (32). ExoU, a cytotoxin, contributes to epithelial cell toxicity, lung injury, and sepsis in infected animals, but the mechanism of its action remains unknown (8,16).While almost all strains of P. aeruginosa appear to possess a set of genes for the TTSS itself (7, 13), not all strains carry genes for all of the four TTS toxins. For instance, strain PAO1 has a negative genotype for exoU and strain PA103 has a negative genotype for exoS (8,9,26). In addition, some chronic isolates suppress the expression of the TTSS (24). It has been reported that patients infected with P. aeruginosa expressing the TTSS had a sixfold higher rate of mortality and an increased incidence of bacteremia than patients infected with P. aeruginosa not expressing the TTSS (24). A poor prognosis for patients with ventilator-associated pneumonia due to P. aeruginosa is associated with strains expressing the TTSS (13). Therefore, characterizing the phenotypes of TTS toxins in P. aeruginosa isolates could help in the identification of virulent strains.The lipopolysaccharide (LPS) O antigen has been used for the classification of P. aeruginosa isolates. There are 20 different International Antigenic Typing Scheme serotypes of P. aeruginosa based on differences of the B-band LPS. Our group previously obtained 108 clinical isolates of P. aeruginosa, and 99 of th...