Revising CX3CR1 Expression on Murine Classical and Non-classical Monocytes

Area of Science:

• Immunology
• Hematology
• Cell Biology

Background:

• Monocytes (Mo) in mice are traditionally classified into classical (CMo) and non-classical (NCMo) subsets.
• This classification is often based on CX3CR1 expression levels, specifically EGFP expression in Cx3cr1^+/ mice, and by analogy with human monocyte subsets.
• The accuracy of using CX3CR1 expression, particularly EGFP levels, to define murine monocyte subsets is questioned.

Purpose of the Study:

• To investigate whether CX3CR1 expression levels reliably discriminate between classical and non-classical monocyte subsets in mice.
• To evaluate the correlation between EGFP expression in Cx3cr1^+/ mice and actual CX3CR1 expression on monocytes.
• To identify alternative markers for accurate murine monocyte subset identification.

Main Methods:

• Unsupervised multiparametric analysis of blood monocytes.
• Analysis performed under steady-state conditions and following sterile peritonitis.
• CX3CR1 expression was measured using a fluorescently-labeled CX3CL1 chemokine and a CX3CR1-specific antibody.

Main Results:

• CX3CR1 expression levels did not effectively differentiate between classical and non-classical monocyte subsets.
• EGFP levels in Cx3cr1^+/ mice were found to be an unreliable indicator of true CX3CR1 expression.
• Ly6C and CD43 combination emerged as a more reliable marker for distinguishing monocyte subpopulations.

Conclusions:

• The conventional classification of murine classical and non-classical monocytes based on CX3CR1 expression (low/high) is potentially inaccurate.
• Researchers should exercise caution when using CX3CR1 expression, particularly EGFP levels, as a sole discriminatory marker.
• The combination of Ly6C and CD43 is recommended as a more reliable alternative for identifying murine monocyte subsets.