Differentiation of monocytes to macrophages induced by influenza virus-infected apoptotic cells

Area of Science:

• Virology
• Immunology
• Cell Biology

Background:

• Monocytes differentiate into macrophages, crucial immune cells involved in host defense.
• Apoptosis, or programmed cell death, plays a role in tissue homeostasis and immune regulation.
• Influenza virus (IV) infection can induce cellular apoptosis.

Purpose of the Study:

• To investigate the effect of culture supernatant from influenza virus (IV)-infected apoptotic and non-apoptotic cells on monocyte differentiation.
• To determine if IV-induced apoptosis in specific fetal membrane cells influences monocyte-to-macrophage differentiation.

Main Methods:

• Human fetal membrane chorion and amnion cells were cultured and infected with IV.
• Culture supernatants from infected and non-infected cells were collected.
• The human monocytic leukemia cell line THP-1 was used to assess differentiation via adhesion assays.
• Morphological analysis and latex particle phagocytosis assays were performed.
• RT-PCR was used to analyze the expression of scavenger receptor mRNA.

Main Results:

• IV infection induced apoptotic DNA fragmentation in chorion cells but not amnion cells.
• Culture supernatant from IV-infected chorion cells induced THP-1 cell adhesion, spreading, and phagocytosis, characteristic of macrophages.
• Culture supernatant from IV-infected amnion cells did not induce these changes.
• Incubation with supernatant from IV-infected chorion cells induced class A scavenger receptor mRNA expression in THP-1 cells.

Conclusions:

• Apoptotic cells resulting from IV infection release soluble factors.
• These soluble factors promote the morphological and functional differentiation of monocytes (THP-1 cells) into macrophages.
• This suggests a novel mechanism by which viral infection and apoptosis can modulate immune cell populations.