Yonsei Med J.  2011 Jul;52(4):624-629. 10.3349/ymj.2011.52.4.624.

Lack of Effect of Dexamethasone on Growth of Orientia Tsutsugamushi Gilliam in Mouse L929 Cells

• Kim CO
• Huh AJ
• Yeom JS
• Lee KS
• Chin BS
• Han SH
• Jeong SJ
• Choi JY
• Song YG
• Kim JM

• KMID: 1727995
• DOI: http://doi.org/10.3349/ymj.2011.52.4.624

Abstract

PURPOSE
Previous studies and our own clinical experience suggest that concurrent corticosteroid treatment for severe rickettsial disease with multiorgan failure may improve the clinical course or reduce mortality. However, the use of corticosteroids as adjunctive treatment for rickettsial diseases is controversial. We attempted to determine the influences of corticosteroid on the growth of Orientia tsutsugamushi in vitro to justify and evaluate the clinical applicability of corticosteroid in rickettsial disease.
MATERIALS AND METHODS
L929 cells were infected with Orientia tsutsugamushi Gilliam. Dexamethasone was added to the cells at final concentrations of 10(1) and 10(7) pg/mL. Cultures were incubated at 35degrees C and processed for flow cytometry on the 6th day after addition of dexamethasone.
RESULTS
Observation on the 6th day after treatment with dexamethasone in infected cultures revealed that there was no difference in fluorescence intensity among the treatment wells. Treatment of the cells with dexamethasone at concentrations of 10(1) and 10(7) pg/mL showed no influence on the growth of Orientia tsutsugamushi.
CONCLUSION
Our results to show that isolated corticosteroid does not enhance the replication of Orientia tsutsugamushi in vitro. Concurrent use of anti-inflammatory or immunosuppressive doses of corticosteroids in conjunction with antibiotics may not have detrimental effects on the course of scrub typhus.

Keyword

Orientia tsutsugamushi; L929 cells; corticosteroids; interferon

MeSH Terms

Animals
Cell Line
Cell Proliferation/drug effects
Dexamethasone/*pharmacology
Flow Cytometry
Interferon-gamma/pharmacology
Mice
Orientia tsutsugamushi/*drug effects/growth & development
Scrub Typhus/drug therapy/microbiology

Figure

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  Fig. 1 Morphological changes of L929 cells after steroid treatment (phase contrast microscopy, ×100). L929 cells uninfected with Orientia tsutsugamushi (A), infected L929 cells (B), and L929 cells treated with dexamethason 105 pg/mL (C) after infection were cultured. At 24-hr intervals from 24 hr to 96 hr, gross morphology of L929 cells was examined by phase contrast microscopy.

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  Fig. 2 Effect of steroid concentrations on the growth of L929 cells. L929 cells were cultured for 10 days with various concentrations of corticosteroids and the number of cells was enumerated. The results showed that during 1-7 days of culture.

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  Fig. 3 Effect of steroid on the growth of Orientia tsutsugamushi. Corticosteroid concentration was raised from 101 pg/mL to 107 pg/mL by 10-fold. The growth level of Orientia tsutsugamushi was evaluated by flow cytometry.

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  Fig. 4 Effect of IFN-γ on the growth of Orientia tsutsugamushi. To evaluate the stability of our results, experiments that assessed the effect of interferon-γ on the growth of Orientia tsutsugamushi by flow cytometry were used as the control group.

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