Cell Biology of Chlamydia in pictures


Fig 1. Title slide. This presentation © Dan Rockey 2002.	Fig 2. Chlamydia is not a tropical flower! Sidewalk advertisement somewhere in the US.	Fig 3. Chlamydial pathogenesis. Step 1: attachment and entry.	Fig 4. Attachment and early development. 1 & 2: Binding to cell surface. 3 & 4 Ingestion into a tight endocytic vesicle. 5 & 6 Differentiation to RB form. 7 to 9. Binary fission of RBs. See: Development in pictures. Also: Regulation of development.

Fig 5. Attachment and entry. Host cell attachment receptors include the mannose receptor (for glycosylated proteins like MOMP); Fc receptor (for antibody coated chlamydiae) and heparan sulphate. The chlamydial endosome avoids fusion with cell lysosomes. In the case of Chlamydia but not Chlamydophila, endosomes fuse with each other to form a larger inclusion.	Fig 6. Conventional cells used to grow chlamydia in the laboratory are not polarised. In reality, chlamydia grow in polarised epithelial cells, with distinct surface and sides, like these Hec1B endometrial cells used by Dr Priscilla Wyrick. Polarised cells have some different properties. See: Protein disulphide isomerase.	Fig 7. Chlamydial pathogenesis. Step 2: Directed remodelling of the intracellular environment.	Fig 8. Strategies used by various facultative or obligate intracellular bacteria to escape the host cell response / lysosomes. Rickettsia etc escape from the endosome into the cytoplasm; Coxiella and Leishmania tolerate and resist fusion of the lysosome with the endosome. Chlamydia like virulent Mycobacteria alter the endosome so that it does not fuse with lysosomes.

Fig 9. Inclusion development in Chlamydophila psittaci and pneumoniae. This vacuole is similar in some ways, but slightly different in other ways, from that formed by Chlamydia. It is likely that each species occupies a vacuole that is somewhat distinct from the others.	Fig 10. Neither early or late endosomes, nor lysosomes, fuse with the chlamydial inclusion as their characteristic markers (shown) are absent. Instead the chlamydial inclusion expands by fusion with sphingomyelin containg lipids derived from the Golgi apparatus in the exocytosis of vesicles.	Fig 11. Ted Hackstadt's proof that C. trachomatis inclusions intercept exocytic vesicle traffic. The top picture is a light micrograph showing an immature double lobed inclusion immediately left of the host cell nucleus. The bottom picture, a black and white print of a fluorescence micrograph, shows that fluorescent labelled lipid (ceramide) of the exocytic pathway derived from the Golgi apparatus, is covering the region of the inclusion.	Fig 12. Chlamydiae have to transport proteins across their own outer envelope and, in the case of inc proteins, into the surrounding inclusion membrane and, at least in some cases, in contact with the host cell cytoplasm. Most attention has focussed on type 3 secretion mechanisms as, in organisms like Shigella they are associated with pathogenicity. However type 2 and 5 mechanisms are probably also important. Much is still unknown about chlamydial secretion pathways.

Fig 13. Carbon replica electron micrograph showing a cluster of chlamydial projections apparently penetrating the surrounding inclusion membrane. These projections are a possible, but not proven, type 3 secretion mechanism for injecting chlamydial proteins across the membrane into the host cell. See: reticulate body structure.	Fig 14. Some chlamydial proteins thought to be associated with inclusion and other host cell membrane & possibly secreted by a type 3 mechanism through chlamydial projections & CopN. Protein 14.3.3 binds to IncD and interacts with MAPK host cell signalling systems [See: 14.3.3]. Embedded IncA may cause fusion of C. trachomatis endosomes [Fig 18]. Exported Cap1 binds to MHC class 1 in the cytoplasm to become a target for cytotoxic T cells.	Fig 15. A Fluorescence micrograph of Inc proteins in a cell multiply infected with C. trachomatis (green) and with Chlamydophila pneumoniae (red) and psittaci (red blobs, below), showing that all three types of chlamydiae produce characteristic Inc proteins.	Fig 16. Fluorescence micrograph of a C. caviae (GPIC) infected cell. The chlamydiae are stained with red fluorescing antibody to chlamydial heat shock protein. They are individually surrounded by inclusion membrane containing green IncA, which also extends in tubular structures through the distal cell cytoplasm to another group of inclusions.

Fig 17. Fluorescence micrograph by Dr Marci Scidmore showing how the 14.3.3 protein co-localises with IncG and with the chlamydial inclusion (right). See: Dr Scidmore's presentation.	Fig 18. Fluorescence micrograph by Bob Suchland (Seattle) of cells infected with a mixture of two C. trachomatis isolates, one fluorescing green, one blue. Normally (right) the two strains will fuse, forming mixed blue green inclusions. However some 1 to 2% of isolates do not fuse (left). This has been associated with mutation in the inclusion membrane embedded IncA protein. Other factors may also be involved.	Fig 19. Fluorescence micrograph demonstrating that CT223p, a distinct inclusion membrane protein, may be present or absent independently of IncA. See: Inclusion proteins.	Fig 20. A reminder of Inclusion membrane transported proteins discussed in Fig 14.

Fig 21. Other important chlamydial proteins which become transported into the host cell cytoplasm include CPAF, which helps chlamydiae to evade host cell antigen processing and the dramatically named CADD (Chlamydia protein associating with death domains) which is thought to induce apoptotic release of chlamydiae from the cell. See: apoptosis	Fig 22. Fluorescence micrograph showing the cytoplasmic location in the host cell of the chlamydial protein CPAF. Micrograph kindly provided by Dr G. Zhong.	Fig 23. Some references	Fig 24. Diagram from Dr Ojcius (Paris) of Bax-dependent apoptosis {See: Bax]. Bax is a caspase independent inducer of apoptosis. Ideally located in the host cell cytoplasm to detect infection-related stress, Bax translocates to the mitochondria, leading to apoptosis. C. caviae-induced apoptosis is inhibited by cells overexpressing Bax-inhibitor 1 or Bcl2.

Fig 25. DNA fragmentation due to apoptosis in C. caviae (GPIC) infected cells.	Fig 26.Chlamydial pathogenesis. Step 3: Persistence and dissemination.	Fig 27. Carbon replica and conventional electron micrograph by A. Matsumoto, showing the enlarged aberrant forms of chlamydial RB associated with chlamydial persistence and with chlamydiae under stress. Such forms may be induced by interferon gamma treatment of the host cell.	Fig 28. Similar aberrant chlamydial growth induced by penicillin. The aberrant chlamydial inclusion still intercepts exocytic lipid vesicle from the Golgi. This is shown here by the continued trafficking of fluorescent ceramide to the inclusion.

Fig 29. Chlamydial pathogenesis. Step 4: The host response.	Fig 30. Diagram by Mahony and Coombes of possible host cell responses to C. pneumoniae infection of blood vessels. The diagram includes both immune and atherogenic responses.	Fig 31.Reference list, see below.	Fig 32. Dan Rockey's team in the Dept of Microbiology at Oregon State University, Corvallis, Oregon, USA.

Chlamydial cell biology in pictures

Presentation by Dan Rockey (Oregon State University)

References