Early endotoxin tolerance is associated with alterations in bone marrow-derived macrophage precursor pools

Area of Science:

• Immunology
• Cell Biology

Background:

• Early endotoxin tolerance is a transient hyporesponsive state following lipopolysaccharide (LPS) exposure.
• The underlying cellular mechanisms of this phenomenon remain largely unknown.

Purpose of the Study:

• To investigate the cellular mechanisms responsible for early endotoxin tolerance.
• To identify changes in bone marrow cell populations during the tolerant state.

Main Methods:

• Established an early tolerance system in mice using a sublethal dose of E. coli K235 LPS.
• Analyzed bone marrow cell populations using cell-sizing and density gradient sedimentation.
• Examined cell cytology to identify progenitor cell types.

Main Results:

• Maximal hyporesponsiveness occurred 3-4 days post-LPS injection, with recovery by day 8.
• Acquisition and maintenance of tolerance correlated with an increased number of bone marrow macrophage progenitor cells.
• Tolerized mice showed an enrichment of larger bone marrow cells, identified as immature monocytic types, containing increased progenitor cells.
• Increased macrophage progenitors persisted after a secondary LPS challenge.

Conclusions:

• Early endotoxin tolerance is associated with an expansion of bone marrow macrophage progenitor cells.
• The hyporesponsiveness during this period may stem from the inability of these immature monocytic cells to respond to LPS.