Microglial Activation After Systemic Stimulation With Lipopolysaccharide and Escherichia coli

Area of Science:

• Neuroscience
• Immunology
• Microbiology

Background:

• Microglial activation is implicated in sepsis-associated delirium.
• Distinct microglial responses to live bacteria versus lipopolysaccharide (LPS) have been suggested.
• This study models microglial activation following live Escherichia coli (E. coli) infection and compares it to LPS challenge.

Purpose of the Study:

• To investigate and compare microglial activation patterns in response to live E. coli infection versus LPS administration in a mouse model.
• To determine the temporal dynamics and intensity of neuroinflammation induced by E. coli compared to LPS.
• To establish which model more closely mimics clinical infection-associated delirium.

Main Methods:

• Mice were challenged with live E. coli or LPS, with control groups receiving saline.
• Microglial activation was assessed using immunohistochemistry (Iba-1) and flow cytometry (cell size, CD45, CD11b).
• Cerebral inflammatory mediator mRNA expression (TNF-α, IL-1β, MCP-1) was quantified.

Main Results:

• E. coli infection induced microglial activation at 72 hours post-inoculation, characterized by increased cell number and size, and CD45 expression, but not CD11b.
• LPS stimulation resulted in earlier (48 hours) and more robust microglial activation, with increased cell number, size, CD45, and CD11b expression.
• While E. coli caused a delayed and less pronounced inflammatory response, LPS significantly upregulated TNF-α, IL-1β, and MCP-1 mRNA levels.

Conclusions:

• Systemic E. coli infection elicits a delayed and less vigorous neuroinflammatory response compared to LPS.
• The E. coli model provides a more clinically relevant representation of infection-associated delirium than LPS stimulation.
• Differences in microglial activation highlight the complexity of neuroinflammation in response to varying infectious agents.