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Immunogenic properties of Pseudomonas aeruginosa mucoid exopolysaccharide
C V Garner1, D DesJardins, G B Pier
1Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115.
Abstract:
Previous studies have shown that antibodies to Pseudomonas aeruginosa mucoid exopolysaccharide (MEP) can be divided into two types on the basis of their functional activity. One type is able to mediate opsonic killing in conjunction with leukocytes and complement, and the other type is not. We investigated, in mice, the properties of this antigen associated with elicitation of opsonic killing antibody. We found that smaller-sized material (Kav = 0.26), which has been tested as a human vaccine, elicited opsonic killing antibody in mice at low doses (1 to 10 micrograms) and at doses of greater than or equal to 40 micrograms, only nonopsonic killing antibody was produced. A similar dose effect was seen with heat-killed mucoid P. aeruginosa cells. After immunization with high doses of this MEP or the heat-killed cells, the mice were refractory to induction of opsonic killing antibody no matter what dose of MEP was used as a booster. In contrast, a larger-molecular-weight preparation (Kav = 0.05) elicited opsonic killing antibody over a wide dose range (1 to 400 micrograms). Additionally, 50 micrograms of the larger-sized preparation could overcome the suppression induced by 50 micrograms of the smaller material. Suppression elicited by 50 micrograms of the smaller material could be adoptively transferred to nonimmune mice with the T-cell fraction of spleen cells. These results indicate that both molecular size and dose are critical determinants for eliciting opsonic killing antibody to mucoid P. aeruginosa after immunizing with MEP.
Insights
Molecular size and dose are critical for eliciting opsonic killing antibodies against Pseudomonas aeruginosa mucoid exopolysaccharide (MEP). Smaller MEP elicits nonopsonic antibodies at high doses, causing suppression, while larger MEP induces opsonic antibodies across a wide dose range.
Area of Science:
- Immunology
- Microbiology
- Vaccine Development
Background:
- Antibodies to Pseudomonas aeruginosa mucoid exopolysaccharide (MEP) exhibit distinct functional activities, including opsonic and nonopsonic killing.
- Previous research has categorized these antibodies based on their ability to mediate bacterial killing with host immune components.
Purpose of the Study:
- To investigate the properties of Pseudomonas aeruginosa mucoid exopolysaccharide (MEP) that determine the elicitation of opsonic killing antibodies in a murine model.
- To elucidate the roles of molecular size and dosage in the immunogenicity of MEP.
Main Methods:
- Immunization of mice with varying doses of smaller (Kav = 0.26) and larger (Kav = 0.05) molecular weight MEP preparations.
- Assessment of antibody functional activity (opsonic vs. nonopsonic killing) following immunization.
- Investigation of dose-dependent effects and the induction of immune suppression.
- Adoptive transfer of T-cells to assess the mechanism of suppression.
Main Results:
- Smaller MEP elicited opsonic antibodies at low doses (1-10 µg) but nonopsonic antibodies at higher doses (≥40 µg).
- High-dose immunization with smaller MEP or heat-killed bacteria induced refractoriness to opsonic antibody induction.
- Larger MEP elicited opsonic antibodies across a broad dose range (1-400 µg).
- The larger MEP preparation could overcome suppression induced by the smaller MEP, which was mediated by T-cells.
Conclusions:
- Both molecular size and dose of MEP are critical factors in determining the type of antibody response (opsonic vs. nonopsonic) elicited.
- Immune suppression associated with high-dose, smaller MEP is T-cell dependent.
- Understanding these parameters is crucial for the rational design of effective vaccines targeting Pseudomonas aeruginosa.