Degree Name

PhD (Doctor of Philosophy)

Program

Biomedical Sciences

Date of Award

5-2008

Committee Chair or Co-Chairs

Priscilla B. Wyrick

Committee Members

David A. Johnson, David L. Williams, J. Russell Hayman, Robert V. Schoborg

Abstract

Chlamydia trachomatis serovars D-K are the leading cause of bacterially-acquired sexually transmitted infections in the United States. As an obligate intracellular pathogen, C. trachomatis infects columnar epithelial cells of the genital mucosae and can cause deleterious sequelae such as pelvic inflammatory disease, infertility, and ectopic pregnancy. Several chlamydial antigens reach the host cell cytosol prior to the natural release of chlamydiae at the end of the developmental cycle. While some of these extra-inclusion antigens traffic to the host cell surface, others remain intracellular where they are proposed to influence vital host cell functions and antigen trafficking and presentation. The research herein examines the escape and trafficking of the immunodominant chlamydial antigens MOMP, LPS, and cHsp60 within C. trachomatis serovar E-infected polarized human endometrial epithelial cells. Studies using high-resolution transmission electron microscopy (TEM) and immuno-TEM report the novel escape mechanism of chlamydial antigens via vesicles everted/pinched off from the inclusion membrane, an occurrence observed both in the presence and absence of the antibiotic azithromycin. These extra-inclusion vesicles were differentiated from Golgi vesicles and were shown to deliver chlamydial heat shock protein 60 (cHsp60)-homologs 2 and 3, but not homolog 1, to the infected cell surface. Examination of the iron-responsiveness of the three cHsp60 homologs by immuno-TEM revealed a significant increase in cHsp60-2 following iron deprivation. Further investigation of the trafficking of chlamydial MOMP and LPS antigens enveloped within the protective everted inclusion membrane vesicles within host cells involved density gradient centrifugation for the separation of epithelial secretory pathway components followed by SDS-PAGE and Western blot to determine whether the chlamydial antigen-containing vesicles could fuse with and deliver the antigens to host cell organelles. Coupled with immuno-TEM, these data confirmed the presence of major chlamydial antigens within the endoplasmic reticulum of infected host cells. Additionally, chlamydial lipopolysaccharide (LPS) was co-localized with CD1d, a lipid antigen-presenting molecule. Collectively, these studies (i) establish a novel escape mechanism for chlamydial antigens, (ii) identify cHsp60-2 as a marker of iron stress response in C. trachomatis, and (iii) define for the first time the host cell ER as a destination for selected chlamydial antigens during infection.

Document Type

Dissertation - Open Access

Copyright

Copyright by the authors.

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