Comparative analysis of monocyte subsets in the pig

Area of Science:

• Immunology
• Comparative genomics
• Cell biology

Background:

• Monocytes are key immune cells with distinct subpopulations in humans and mice, defined by surface markers like CD14/16 and Ly6C/CX3CR1.
• Understanding monocyte heterogeneity is crucial for immunology and disease research.
• Previous research suggested functional equivalence of monocyte subsets across species, but species-specific gene expression patterns have been noted.

Purpose of the Study:

• To identify and characterize monocyte subpopulations in pigs.
• To compare pig monocyte subsets with those in humans and mice.
• To investigate the role of CSF1 in pig monocyte differentiation and gene expression.

Main Methods:

• Isolation and analysis of pig peripheral blood mononuclear cells (PBMCs).
• Flow cytometry for identifying monocyte subpopulations based on CD14 and CD163 expression.
• Cell culture with CSF1 to study differentiation.
• Gene expression profiling using a pig whole genome microarray.

Main Results:

• Two distinct pig monocyte populations, CD14(hi)-CD163(low) and CD14(low)-CD163(hi), were identified with equal abundance.
• CSF1 stimulation induced a maturation series in pig monocytes.
• Gene expression analysis revealed species-specific patterns for certain monocyte-associated genes.
• Pig CD14(low)-CD163(high) monocytes appear functionally equivalent to intermediate human monocytes, lacking a direct counterpart to the human "nonclassical" CD14(-) CD16(+) subset.

Conclusions:

• Pig monocytes can be classified into two main subsets based on CD14 and CD163 expression.
• CSF1 is a key regulator of pig monocyte maturation.
• The pig may not fully recapitulate human monocyte heterogeneity, particularly the nonclassical subset.
• These findings impact the utility of pigs as a model for studying human monocyte biology and diseases.