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Specificity and functional activity of anti-Burkholderia pseudomallei polysaccharide antibodies
M Ho1, T Schollaardt, M D Smith
1Department of Microbiology and Infectious Diseases, University of Calgary, Alberta, Canada.
Abstract:
The lipopolysaccharide (LPS) of Burkholderia pseudomallei, the causative agent of melioidosis, consists of two O-antigenic polysaccharides designated O-PS I and O-PS II. In this study, the O-PS specificity and functional activity of a protective polyclonal antiserum and an immunoglobulin M (IgM) monoclonal antibody were determined. The polyclonal antiserum recognized both O-PS I and O-PS II, while the monoclonal antibody was O-PS II specific. Both mediated phagocytic killing of B. pseudomallei by polymorphonuclear leukocytes. Patients acutely infected with B. pseudomallei also produced antibodies to the two O-PSs, but these antibodies were not produced by asymptomatic individuals from an area of endemicity who were seropositive by an indirect hemagglutination test using sonicated heat-killed whole organisms as antigen. IgM antibodies were detected only in patients with localized infection. IgG antibodies were detected in all acutely infected patients, but there was no significant difference in antibody levels among patients with localized infection, patients who survived septicemic illness, and patients who died from septicemic illness. Further analysis of the IgG response revealed production of IgG1 and IgG2 antibodies by all patient groups, while an IgG3 response was seen only in survivors of septicemic infection. IgG4 was not detectable even when a fivefold-lower serum dilution was used. Patient sera also mediated phagocytic killing by polymorphonuclear leukocytes, and the killing effect was enhanced by complement. These results suggest that antibodies to the LPS O-polysaccharides of B. pseudomallei are protective by promoting phagocytic killing. The antibodies develop during human infection and may facilitate clearance of the organisms, as seen in a diabetic rat model of B. pseudomallei infection.
Insights
Antibodies targeting lipopolysaccharide O-antigenic polysaccharides from Burkholderia pseudomallei enhance bacterial killing by immune cells. These protective antibodies develop during melioidosis infection, aiding organism clearance.
Area of Science:
- Immunology
- Microbiology
- Infectious Diseases
Background:
- Melioidosis is caused by Burkholderia pseudomallei, a bacterium with lipopolysaccharide (LPS) O-antigenic polysaccharides (O-PS I and O-PS II).
- Understanding the immune response to these LPS structures is crucial for developing effective treatments and vaccines.
Purpose of the Study:
- To determine the O-PS specificity and functional activity of protective antibodies against Burkholderia pseudomallei.
- To investigate the antibody profiles in patients with different forms of melioidosis and in asymptomatic individuals.
Main Methods:
- Characterization of a polyclonal antiserum and a monoclonal antibody for their reactivity to O-PS I and O-PS II.
- Assessment of antibody-mediated phagocytic killing of B. pseudomallei by polymorphonuclear leukocytes.
- Analysis of immunoglobulin M (IgM) and immunoglobulin G (IgG) antibody subclasses in patient sera.
Main Results:
- A polyclonal antiserum recognized both O-PS I and O-PS II, while a monoclonal antibody was specific to O-PS II.
- Both antibody types mediated phagocytic killing of B. pseudomallei.
- Patients with acute melioidosis produced antibodies to O-PSs; IgM was detected in localized infections, while IgG subclasses varied among patient groups.
- Patient sera enhanced phagocytic killing, with complement further augmenting this effect.
Conclusions:
- Antibodies to LPS O-polysaccharides of B. pseudomallei are protective, primarily by promoting phagocytic killing.
- These antibodies develop during human infection and may play a role in clearing the organism.
- The findings suggest potential targets for melioidosis vaccine development.