Vaccination againstPseudomonas aeruginosaPneumonia in Immunocompromised Mice

Abstract

Immunocompromised patients are highly susceptible to infection with Pseudomonas aeruginosa. Our laboratory previously showed that intranasal administration of an attenuated Salmonella strain expressing the P. aeruginosa lipopolysaccharide O antigen was effective in clearing bacteria and preventing mortality in wild-type mice after intranasal challenge. We were interested in investigating the efficacy of this vaccine strategy in immunocompromised mice. Mice rendered leukopenic or neutropenic by intraperitoneal treatment with cyclophosphamide (Cy) or RB6-8C5 antibody, respectively, were more susceptible to P. aeruginosa pneumonia than their nontreated counterparts, demonstrating 50% lethal doses several logs lower than that in wild-type mice. This hypersusceptiblity was also associated with bacterial dissemination to the liver and spleen and increased lung permeability in Cy mice. Vaccination of the mice prior to treatment resulted in better survival and lower bacterial loads compared to vector-immunized mice. Although the treatments had no effect on antibody titers, this level of protection was still lower than that seen in untreated vaccinated mice. Administration of antibodies directly to the site of infection at the time of bacterial delivery prolonged survival and lowered bacterial loads in the immunocompromised mice. These results demonstrate the importance of white blood cells while still suggesting a critical role for antibodies in protection against P. aeruginosa infection.Pseudomonas aeruginosa is an important opportunistic pathogen that is associated with infections in cystic fibrosis patients, burn patients, patients on ventilators, and contact lens wearers. Another important infection group consists of immunocompromised individuals, such as those undergoing chemotherapy or AIDS patients (11,14,17). Infections in these patient populations are difficult to treat, partly due to the innate antibiotic resistance of P. aeruginosa and partly due to the immunocompromised status of the patient. A particular problem associated with pneumonia in immunocompromised patients is bacteremia, which allows the bacteria to spread to other organs (11,14,17).Recently, host factors contributing to dissemination of P. aeruginosa were investigated with a gastrointestinal model of colonization leading to infection (12). Mice previously infected with P. aeruginosa in the intestinal tract and then rendered neutropenic had increased dissemination and mortality. Two methods of inducing of neutropenia were used in that study (12): treatment with cyclophosphamide (Cy) and treatment with the RB6-8C5 antibody specific for the Ly6 antigen on the surface of neutrophils (9). Neutropenic mice were also used by Vance et al. (24) as a model to monitor dissemination of type III secretion system (TTSS) mutants of P. aeruginosa.Previous work in our laboratory characterized a vaccine that confers serotype-specific protection against P. aeruginosa challenge (5). The vaccine consists of Salmonella enterica serovar Typhimurium strain SL3261, an ...

Four-Component Staphylococcus aureus Vaccine 4C-Staph Enhances Fcγ Receptor Expression in Neutrophils and Monocytes and Mitigates S. aureus Infection in Neutropenic Mice

“…5), suggesting that innate cells other than neutrophils may compensate for the neutropenia condition and contribute to protection from the infection. This result is consistent with the observation that an increase of monocytes has been observed in humans experiencing some neutropenic conditions (31) and significantly enriches previous observations reported for immunosuppressed mice immunized with a Pseudomonas aeruginosa live attenuated vaccine (36,37).…”

Activated β2 Integrins Restrict Neutrophil Recruitment during Murine Acute Pseudomonal Pneumonia

“…Neutropenic human patients (39,40) and laboratory mice (36,41,42) have enhanced susceptibility to pseudomonal pneumonia. Inefficient rapid, early neutrophil recruitment, even when corrected within 24 hours, resulted in 10-fold more bacteria in the airspaces at 48 hours in a murine model of pneumococcal pneumonia (43).…”

Inescapable Need for Neutrophils as Mediators of Cellular Innate Immunity to Acute Pseudomonas aeruginosa Pneumonia

“…In contrast, it is generally well-accepted that neutrophils comprise a major component of host resistance to P. aeruginosa infection, particularly in the acute settings of bacteremia and sepsis (32). Neutrophil depletion (49,55) or inhibition of PMN recruitment to the lungs by blocking CXC chemokine receptor 2 (58) resulted in increased mortality after P. aeruginosa infection, but these studies used high doses of single strains of P. aeruginosa that were chosen due to their known high virulence in the setting of murine pneumonia and did not encompass a systematic study of the relationship of PMN depletion to resultant infectious doses of multiple isolates of P. aeruginosa that could cause pneumonia, sepsis, and death. Nor did these studies rule out additional effects from their interventions on disruption of local mediators of immunity, such as AM function or mucociliary clearance, contributing to some of the enhanced susceptibility to P. aeruginosa pneumonia.…”

“…Similarly, others have previously established that neutropenia induced by either Cy or MAb RB6-8C5 lowers the inoculum of P. aeruginosa needed to produce pneumonia and sepsis (49,55), but no systematic study of the relative contributions of neutrophils versus other mediators of innate immunity were analyzed. Again, only one strain of P. aeruginosa for each treatment was used in these other studies, whereas we used a range of strains, including numerous clinical isolates, and the inoculum used in one of these studies was also substantially higher (1 ϫ 10 6 CFU) (55).…”