Even ephemeral endotoxin exposure establishes endotoxin tolerance

Area of Science:

• Immunology
• Cellular Biology
• Molecular Biology

Background:

• Macrophages exposed to lipopolysaccharide (LPS) develop endotoxin tolerance, characterized by reduced extracellular signal-regulated kinase (ERK) activation upon rechallenge.
• Prior studies indicated that LPS pretreatment (21 hours) at 1 ng/mL augmented TNF release, while 100 ng/mL inhibited it.
• Endotoxin tolerance is linked to altered ERK and p38 kinase activation following LPS restimulation.

Purpose of the Study:

• To investigate how the time interval between LPS pretreatment and rechallenge influences macrophage responses.
• To determine the impact of LPS dose and pretreatment duration on macrophage activation and cytokine secretion.

Main Methods:

• RAW 264.7 cells were pretreated with varying LPS concentrations (0, 1, 10, 100 ng/mL) for 4 hours.
• Cells were subsequently rechallenged immediately or after a 21-hour interval with different LPS doses.
• Tumor necrosis factor (TNF) secretion was measured via ELISA, and active phospho-ERK levels were assessed by Western blot.

Main Results:

• A 21-hour interval post-pretreatment showed LPS augmentation (1 ng/mL) or inhibition (100 ng/mL) of TNF release.
• Immediate rechallenge resulted in additive effects with 100 ng/mL LPS and no significant change with 1 ng/mL LPS.
• Western blot analysis revealed that immediate rechallenge prevented ERK activation in 'tolerant' macrophages.

Conclusions:

• Short LPS exposure alters macrophage ERK activation, but longer intervals are necessary for modified cytokine release.
• Both the dose of LPS used for pretreatment and the interval before rechallenge are critical factors modulating macrophage responsiveness.