Chlamydia pneumoniae uses the mannose 6-phosphate/insulin-like growth factor 2 receptor for infection of endothelial cells
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Updated: Mar 16, 2026
Pneumococcus Infection of Primary Human Endothelial Cells in Constant Flow
Published on: October 31, 2019
Mirja Puolakkainen1, Cho-Chou Kuo, Lee Ann Campbell
1Department of Pathobiology, Box 357238, University of Washington, Seattle, WA 98195, USA.
Abstract:
Several mechanisms for attachment and entry of Chlamydia have been proposed. We previously determined that the major outer membrane protein of Chlamydia trachomatis is glycosylated with a high-mannose oligosaccharide, and a similar structure inhibited the attachment and infectivity of C. trachomatis in epithelial cells. Because insulin-like growth factor 2 (IGF2) was shown to enhance the infectivity of Chlamydia pneumoniae but not C. trachomatis in endothelial cells, a hapten inhibition assay was used to analyze whether the mannose 6-phosphate (M6P)/IGF2 receptor that also binds M6P could be involved in infection of endothelial cells (HMEC-1) by Chlamydia. M6P and mannose 6-phosphate-poly[N-(2-hydroxyethyl)-acrylamide] (M6P-PAA) inhibited the infectivity of C. pneumoniae AR-39, but not C. trachomatis serovar UW5 or L2, while mannan inhibited the growth of C. trachomatis, but not C. pneumoniae. Using metabolically labeled organisms incubated with cells at 4 degrees C (organisms attach but do not enter) or at 37 degrees C (organisms attach and are internalized), M6P-PAA was shown to inhibit attachment and internalization of C. pneumoniae in endothelial cells but did not inhibit attachment or internalization of C. trachomatis serovar E or L2. These findings indicate that C. pneumoniae can utilize the M6P/IGF2 receptor and that the use of this receptor for attachment and entry differs between C. pneumoniae and C. trachomatis.
Insights
Chlamydia pneumoniae uses the mannose 6-phosphate/IGF2 receptor for attachment and entry into endothelial cells, unlike Chlamydia trachomatis. This receptor usage differs significantly between these two Chlamydia species.
Area of Science:
- Microbiology
- Cell Biology
- Infectious Diseases
Background:
- Chlamydia species exhibit varied mechanisms for host cell attachment and entry.
- Previous work identified a high-mannose oligosaccharide on Chlamydia trachomatis outer membrane protein, inhibiting its infectivity.
- Insulin-like growth factor 2 (IGF2) enhances Chlamydia pneumoniae, but not Chlamydia trachomatis, infectivity in endothelial cells.
Purpose of the Study:
- To investigate the role of the mannose 6-phosphate (M6P)/IGF2 receptor in the infection of human microvascular endothelial cells (HMEC-1) by Chlamydia species.
- To determine if Chlamydia pneumoniae utilizes the M6P/IGF2 receptor for cellular entry.
- To compare the receptor usage for attachment and entry between Chlamydia pneumoniae and Chlamydia trachomatis.
Main Methods:
- Hapten inhibition assays were performed using M6P and M6P-poly[N-(2-hydroxyethyl)-acrylamide] (M6P-PAA) to block receptor binding.
- Mannan was used as a control inhibitor.
- Metabolically labeled Chlamydia organisms were incubated with endothelial cells at 4°C (attachment) and 37°C (internalization) to assess attachment and entry inhibition.
Main Results:
- M6P and M6P-PAA inhibited the infectivity of Chlamydia pneumoniae but not Chlamydia trachomatis serovars UW5 or L2.
- Mannan inhibited Chlamydia trachomatis but not Chlamydia pneumoniae.
- M6P-PAA significantly inhibited both the attachment and internalization of Chlamydia pneumoniae in endothelial cells, while having no effect on Chlamydia trachomatis serovars E or L2.
Conclusions:
- Chlamydia pneumoniae employs the M6P/IGF2 receptor for attachment and entry into endothelial cells.
- The mechanisms of attachment and entry, specifically the utilization of the M6P/IGF2 receptor, are distinct between Chlamydia pneumoniae and Chlamydia trachomatis.
- These findings highlight species-specific differences in Chlamydia-host cell interactions.
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