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Advisory Committee Chair

Moon H Nahm

Advisory Committee Members

T Prescott Atkinson

William H Benjamin, Jr

Chad Steele

Janet Yother

Document Type

Dissertation

Date of Award

2014

Degree Name by School

Doctor of Education (EdD) School of Education

Abstract

Streptococcus pneumoniae (pneumococcus) is a significant human pathogen that typically resides in the nasopharynx of humans. The major virulence factor of pneumococcus is its capsular polysaccharide, of which it can express over 90 unique serotypes. However, there is great disparity in which serotypes colonize or cause disease, though the reason for these differences are not well understood. Serotype 11A is one such serotype that frequently colonizes the nasopharynx of children, but rarely causes disease. Interestingly, serotype 11E, a variant of 11A, varies only in the O-acetylation of a galactose residue in its polysaccharide repeating unit. This difference in structure is due to inactivation of wcjE, which encodes a putative O-acetyltransferase. Each 11E strain has a unique mutation of its wcjE allele. Moreover, 11E is rarely found in carriage, but is more commonly found among invasive disease isolates. Thus, we hypothesized that upon invasion, 11A en-counters some selective pressure and microevolves into 11E. We sought to determine what host factor may be driving this selection. We found an innate opsonin, called ficolin-2, could bind to serotype 11A, but not 11E. Ficolin-2 is an activator of the lectin complement pathway and binds acetylated ligands. We found that ficolin-2 can bind to many pneumococcal serotypes that express WcjE-mediated O-acetylation, and loss of WcjE-mediated O-acetylation led to loss of binding. Moreover, ficolin-2 was able to me-diate complement deposition and opsonophagocytic killing of serotypes expressing WcjE-mediated O-acetylation (i.e., 11A), but not those lacking WcjE-mediated O-acetylation (i.e., 11E). Our study is the first to show the specific ligand ficolin-2 recognizes on the surface of pneumococci and the first to provide in vitro and in vivo evidence for the role of ficolin-2 during pneumococcal disease. Also while studying ficolin-2, we discovered several useful tools. We found that plastic blood collection tubes contain an inhibitor that affects functional ficolin-2 levels. This inhibitor can be eluted and used to specifically inhibit ficolin-2 binding. We also found that complement component-depleted sera are unexpectedly co-depleted of ficolin-2. Supplementation of the depleted sera with recombinant ficolin-2 allows ficolin-2-mediated complement deposition. Thus, these findings provide unique tools for studying ficolin-2 mediated pathways.

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