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Dissertation/Thesis Abstract

Polyreactive and Antigen-specific B-cell Response to Streptococcus pneumoniae
by Thompson, Rebecca S., Ph.D., The University of Toledo, 2012, 0; 3509863
Abstract (Summary)

Streptococcus pneumonia is a prevalent cause of disease and mortality worldwide. Pneumococcal disease includes pneumonia, otitis media, bacteremia and meningitis. Antibodies against the pneumococcal capsular polysaccharide are protective and aid in clearance of the bacteria.

The phenotype of human anti-pneumococcal polysaccharide (PPS) B cells has not been well characterized. Immune-compromised individuals often respond poorly to the 23-valent purified pneumococcal polysaccharide vaccine (PPV) and are often deficient in IgM memory and switched memory IgM cells. We hypothesized that the anti-PPS B cells which respond to PPV are IgM memory cells. To directly characterize anti-PPS B cells, fluorescently labeled PPS14 and PPS23F in conjunction with a FACSAria flow cytometer were used to detect and characterize PPS-specific B cells from healthy young adult volunteers pre- and post-vaccination with PPV. Post-vaccination PPS-specific B cells expressed a dominant IgM memory phenotype, CD27+IgM +, suggesting a key role of IgM memory cells in the immune response to PPS. These results help explain the poor PPS-specific antibody response post-vaccination in individuals deficient in IgM+/CD27 + B cells.

When PPS-specific antibodies are not present, natural antibodies serve as the body's first line of defense against pneumococcal challenge. These low avidity, polyreactive anti-PPS antibodies have not been extensively studied in humans. We hypothesized that while these antibodies are low avidity, they elicit protection against pneumococcal challenge. In this project, PPS binding B cells were isolated using fluorescently labeled PPS and expanded in tissue culture. Although these antibodies were isolated from individual B cells and possessed unique VH/VL, sequence analysis and avidity studies revealed similar characteristics. The VL CDR3 was restricted in length and VH CDR3s expressed a statistically higher number of flexible amino acids when compared to PPS-specific antibodies. To investigate the role of the constant region in antibody avidity, these polyreactive variable regions were expressed as IgG1 or IgG2. Kinetic analysis demonstrated that IgG1 antibodies were more avid when compared to IgG2. The IgG1 isotype is more flexible than IgG2 allowing unrestricted movement to bind PPS antigens more avidly. Our results suggest IgM + memory cells respond to PPV and polyreactive antibodies possess specific characteristics that enable recognition of multiple PPS.

Indexing (document details)
Advisor: Westerink, M. A. Julie
Commitee: Dignam, David, Malhotra, Deepak, Ruch, Randall, Wooten, Mark
School: The University of Toledo
Department: College of Health Science and Human Service
School Location: United States -- Ohio
Source: DAI-B 73/09(E), Dissertation Abstracts International
Subjects: Cellular biology, Microbiology, Medicine, Immunology
Keywords: Antibody, B cells, Igm memory, Isotype, Polyreactive, Streptococcus pneumoniae
Publication Number: 3509863
ISBN: 978-1-267-36813-3
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