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Infection and Immunity, May 2002, p. 2392-2398, Vol. 70, No. 5
0019-9567/02/$04.00+0     DOI: 10.1128/IAI.70.5.2392-2398.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Chlamydia pneumoniae Infection Induces Differentiation of Monocytes into Macrophages

Hiroyuki Yamaguchi, Shusaku Haranaga, Ray Widen, Herman Friedman, and Yoshimasa Yamamoto^*

Department of Medical Microbiology and Immunology, University of South Florida College of Medicine, Tampa, Florida 33612

Received 7 September 2001/ Returned for modification 29 October 2001/ Accepted 30 January 2002

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.

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* Corresponding author. Mailing address: Department of Medical Microbiology and Immunology, University of South Florida College of Medicine, 12901 Bruce B. Downs Blvd., Tampa, FL 33612. Phone: (813) 974-2332. Fax: (813) 974-4151. E-mail: yyamamot{at}hsc.usf.edu.

Editor: B. B. Finlay

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Infection and Immunity, May 2002, p. 2392-2398, Vol. 70, No. 5
0019-9567/02/$04.00+0     DOI: 10.1128/IAI.70.5.2392-2398.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

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