Interaction of human peripheral blood monocytes with apoptotic polymorphonuclear cells

Area of Science:

• Immunology
• Cell Biology

Background:

• Macrophages phagocytose apoptotic neutrophils, but monocyte function is less understood.
• Previous studies suggested monocytes require differentiation into macrophages to phagocytose neutrophils.

Purpose of the Study:

• To investigate the phagocytic capacity of peripheral blood monocytes for apoptotic neutrophils.
• To identify the specific monocyte subsets and molecular mechanisms involved in phagocytosis.

Main Methods:

• Flow cytometry and confocal microscopy were employed.
• Analysis focused on CD14 and CD16 monocyte subsets.
• Investigated the role of CD36 and phosphatidyl-L-serine.

Main Results:

• Peripheral blood monocytes phagocytose apoptotic, but not live, granulocytes.
• CD16(+) monocyte subsets (CD14(high)CD16(+) and CD14(dim)CD16(+)) are primarily involved.
• Phagocytosis requires CD36 and is independent of the CD14 mechanism for neutrophils.
• Uptake of apoptotic Jurkat T cells is CD14 and CD36 dependent.
• Phosphatidyl-L-serine liposomes reduced binding of apoptotic neutrophils.
• Lipopolysaccharide-activated monocytes produced more IL-10 and less TNF-α and IL-1β upon contact with apoptotic cells.

Conclusions:

• Monocytes directly phagocytose apoptotic neutrophils via CD36-dependent pathways.
• Specific CD16(+) monocyte subsets mediate this clearance.
• Monocyte interaction with apoptotic cells modulates cytokine production, favoring an anti-inflammatory response.