Human Monoclonal Antibodies toPseudomonas aeruginosaAlginate That Protect against Infection by Both Mucoid and Nonmucoid Strains

Abstract

Two fully human mAbs specific for epitopes dependent on intact carboxylate groups on the C6 carbon of the mannuronic acid components of Pseudomonas aeruginosa alginate were found to promote phagocytic killing of both mucoid and nonmucoid strains as well as protection against both types of strains in a mouse model of acute pneumonia. The specificity of the mAbs for alginate was determined by ELISA and killing assays. Some strains of P. aeruginosa did not make detectable alginate in vitro, but in vivo protection against lethal pneumonia was obtained and shown to be due to rapid induction of expression of alginate in the murine lung. No protection against strains genetically unable to make alginate was achieved. These mAbs have potential to be passive therapeutic reagents for all strains of P. aeruginosa and the results document that alginate is a target for the proper type of protective Ab even when expressed at low levels on phenotypically nonmucoid strains.

The Exopolysaccharide Alginate Protects Pseudomonas aeruginosa Biofilm Bacteria from IFN-γ-Mediated Macrophage Killing

“…On the surface, our data would seem to contradict this work because isogenic algD Ϫ biofilms of both of these strains were susceptible to human leukocyte killing, whereas the parent, wild-type strains were not. However, two recent articles demonstrated, at least for the PA01 strain, that alginate production is heightened in vivo within 1 h of injection into a mouse (36,51). These data correlate better with the presumed transition from nonmucoid to the mucoid phenotype in the lungs of CF patients likely mediated by reactive oxygen species (52).…”

“…Unfortunately, Abs against P. aeruginosa isolated from CF patients were unable to act as effective opsonins and did not lead to killing and clearance of the biofilm bacteria in vitro (35). Recently, Pier et al (36) demonstrated that a new generation of Abs against alginate promoted clearance of planktonic P. aeruginosa in an acute lung infection model in mice. The opsonic Abs were required for killing and clearance of these organisms.…”

“…A previous study demonstrated that rabbit Abs against alginate led to killing of P. aeruginosa biofilm bacteria but not Abs generated by CF patients (35). The same laboratory demonstrated that a new generation of humanized anti-alginate Abs protected against planktonic, mucoid P. aeruginosa bacteria (36). Despite these recent findings, a direct examination of the role of alginate in P. aeruginosa biofilm resistance to host killing mechanisms has not been reported.…”

Airway epithelial control of Pseudomonas aeruginosa infection in cystic fibrosis

“…However, although animal studies indicate there are potential means to induce these opsonically-active antibodies by vaccination [75], this has not readily been achieved in large-scale human trials. Thus, an alternative approach is being pursued, involving the passive administration of a recently described fully human monoclonal antibody to alginate that is opsonic and protective in animal studies [76]. Future goals of improved immunotherapy might also involve the induction of mucosal immunity, particularly local immunoglobulin G (IgG) [77], before colonization with P. aeruginosa [77], as well as the use of different and multiple antigens as vaccine components.…”

Role of polysaccharides in Pseudomonas aeruginosa biofilm development

“…Alginate appears to protect P. aeruginosa from the consequences of this inflammation, since it scavenges free radicals released by activated macrophages in vitro and appears to provide protection from phagocytic clearance [4,6]. Although antibodies to alginate are found in the sera of chronically infected CF patients, these antibodies fail to mediate opsonic killing of P. aeruginosa in vitro [7]. Likely each of these properties contributes to the ability of mucoid P. aeruginosa to persist and establish chronic infections in the CF lung.…”