Pulmonary infection by Yersinia pestis rapidly establishes a permissive environment for microbial proliferation

Area of Science:

• Microbiology
• Immunology
• Pathogen-host interactions

Background:

• Pneumonic plague, caused by Yersinia pestis, exhibits biphasic disease progression with distinct preinflammatory and proinflammatory phases.
• During the preinflammatory phase, Y. pestis replicates extensively, evading pulmonary defenses.
• The mechanisms underlying Y. pestis-mediated immune evasion during the early stages of infection are not fully understood.

Purpose of the Study:

• To investigate the mechanisms by which Yersinia pestis establishes an immunosuppressive environment during the preinflammatory phase of pneumonic plague.
• To determine the role of the Ysc type III secretion system in Y. pestis-induced immune modulation.
• To identify bacterial factors contributing to the transformation of the lung into a permissive environment for pathogen growth.

Main Methods:

• Coinfection model of pneumonic plague using Yersinia pestis.
• Analysis of Ysc type III secretion system effector function.
• Unbiased negative selection screen of Y. pestis mutants.

Main Results:

• Yersinia pestis actively induces a localized, dominant anti-inflammatory state in the lung.
• This immunosuppression facilitates the survival and rapid growth of Y. pestis and coinfecting avirulent organisms.
• Effectors from the Ysc type III secretion system are required, but not sufficient, for this immunosuppressive effect.
• No known Y. pestis virulence genes were found to be under negative selection, indicating a broad environmental permissiveness.

Conclusions:

• Yersinia pestis transforms the lung into a permissive environment during the preinflammatory phase of pneumonic plague through active immune modulation.
• The Ysc type III secretion system plays a critical role in establishing this immunosuppressive state.
• These findings provide novel insights into the pathogenesis of pneumonic plague and potential therapeutic targets.