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Chlamydia pneumoniae infection induces differentiation of monocytes into macrophages
Hiroyuki Yamaguchi1, Shusaku Haranaga, Ray Widen
1Department of Medical Microbiology and Immunology, University of South Florida College of Medicine, Tampa, Florida 33612, USA.
Abstract:
Migration and differentiation of monocytes to the intima of blood vessels may be a crucial first step in the development of atherosclerosis associated with Chlamydia (Chlamydophila) pneumoniae. However, the involvement of C. pneumoniae infection in such steps is not clear. In the present study, therefore, the differentiation-inducing activity of C. pneumoniae to monocytes was examined. Human THP-1 monocytic cell line cells were infected with C. pneumoniae, and the differentiation of monocytes to macrophages was assessed by cell morphology, phagocytic activity, and expression of a cell surface adhesion molecule. The monocytic cells infected with viable bacteria markedly differentiated into macrophages associated with diffused cell morphology, increased uptake of polystyrene beads and increased ICAM-1 (intercellular adhesion molecule 1) expression on the cell surfaces. Heat-killed bacteria did not induce any morphological changes or increase of phagocytosis, but they did induce an increase of cell surface ICAM-1 expressions in THP-1 monocytic cells. The antibiotic minocycline treatment of infected cells resulted in marked inhibition of the cell differentiation as well as C. pneumoniae growth in the cells, but not ICAM-1 expression. In addition, the experiments with human peripheral blood monocytes infected with C. pneumoniae also showed the differentiation of macrophages assessed by morphological change and phagocytic activity. These results indicate that C. pneumoniae infection may directly induce the differentiation of monocytes to macrophages. However, antigenic stimulation of monocytes with bacteria may not be sufficient for a full macrophage differentiation.
Insights
Chlamydia pneumoniae infection directly promotes monocyte differentiation into macrophages, a key step in atherosclerosis development. This process involves changes in cell morphology and increased ICAM-1 expression, but requires viable bacteria for full effect.
Area of Science:
- Immunology
- Microbiology
- Pathology
Background:
- Monocyte migration and differentiation into macrophages are critical early events in atherosclerosis.
- The specific role of Chlamydia (Chlamydophila) pneumoniae infection in this process remains unclear.
Purpose of the Study:
- To investigate the differentiation-inducing activity of C. pneumoniae on monocytes.
- To understand the mechanisms by which C. pneumoniae influences monocyte-to-macrophage differentiation.
Main Methods:
- Infection of human THP-1 monocytic cells and primary peripheral blood monocytes with C. pneumoniae.
- Assessment of monocyte differentiation via cell morphology, phagocytic activity, and ICAM-1 expression.
- Evaluation of minocycline's effect on differentiation and bacterial growth.
Main Results:
- Viable C. pneumoniae induced significant monocyte differentiation into macrophages, characterized by altered morphology, enhanced phagocytosis, and increased ICAM-1 expression.
- Heat-killed bacteria increased ICAM-1 expression but did not induce morphological changes or enhance phagocytosis.
- Minocycline inhibited both C. pneumoniae growth and monocyte differentiation but not ICAM-1 expression.
Conclusions:
- C. pneumoniae infection directly induces monocyte differentiation into macrophages.
- Viable bacteria are necessary for full differentiation, suggesting a role beyond mere antigenic stimulation.