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Interferon-gamma mediates long-term persistent Chlamydia psittaci infection in vitro
1Moredun Research Institute, Edinburgh, UK.
Abstract:
The long-term anti-chlamydial effects of recombinant ovine interferon gamma (rOvIFN-gamma) were studied in ovine ST-6 fibroblasts infected with the S26/3 strain of Chlamydia psittaci. Chlamydial multiplication was assessed by enzyme-linked immunosorbent assay analysis of supernate lipopolysaccharide, titration of inclusion-forming units in culture supernates, and enumeration of inclusion bodies in cultured cells at 7-day intervals. Concentrations of 250 and 1000 U/ml of rOvIFN-gamma resulted in a microbistatic inhibition of C. psittaci growth, which appeared to become microbicidal when rOvIFN-gamma was maintained in the cultures for 14 days or more. There were no signs of C. psittaci multiplication when cultures were maintained in 25 or 100 U/ml of rOvIFN-gamma. However, subsequent removal of rOvIFN-gamma from these cultures resulted in a re-emergence of viable, infectious chlamydiae, which eventually killed all the fibroblasts. This re-emergence was more rapid in cultures initially treated with 25 U/ml of rOvIFN-gamma than in those treated with 100 U/ml.
Insights
Recombinant ovine interferon gamma (rOvIFN-gamma) shows long-term anti-chlamydial effects. Higher concentrations of rOvIFN-gamma were microbicidal against Chlamydia psittaci, but lower doses allowed pathogen re-emergence.
Area of Science:
- Veterinary Medicine
- Immunology
- Microbiology
Background:
- Chlamydia psittaci is an important veterinary pathogen.
- Interferon gamma is a key cytokine in immune responses.
- Understanding long-term effects of treatments is crucial for disease control.
Purpose of the Study:
- To investigate the long-term anti-chlamydial effects of recombinant ovine interferon gamma (rOvIFN-gamma).
- To determine the minimum effective concentration and duration of rOvIFN-gamma treatment against Chlamydia psittaci.
Main Methods:
- Ovine ST-6 fibroblasts were infected with Chlamydia psittaci.
- Recombinant ovine interferon gamma (rOvIFN-gamma) was applied at various concentrations.
- Chlamydial multiplication was assessed using ELISA, IFU titrations, and inclusion body enumeration.
Main Results:
- rOvIFN-gamma at 250 and 1000 U/ml exhibited microbistatic effects, becoming microbicidal after 14 days.
- Lower concentrations (25 and 100 U/ml) inhibited growth but allowed chlamydiae re-emergence upon removal.
- Re-emergence was faster at 25 U/ml compared to 100 U/ml, leading to fibroblast death.
Conclusions:
- Sustained high-dose rOvIFN-gamma can achieve microbicidal activity against Chlamydia psittaci.
- Intermittent or low-dose rOvIFN-gamma may not provide complete eradication and risks pathogen re-emergence.
- Further research into optimal dosing and duration for effective Chlamydia psittaci treatment is warranted.