Quantifying complement-mediated phagocytosis by human monocyte-derived macrophages

Area of Science:

• Immunology
• Cell Biology
• Virology

Background:

• Complement-mediated phagocytosis is essential for immune surveillance.
• Human immunodeficiency virus type 1 (HIV-1) infects macrophages, key players in the immune system.
• The impact of HIV-1 on complement receptor-mediated phagocytosis by macrophages remains incompletely understood.

Purpose of the Study:

• To investigate the role of complement receptors in the phagocytosis of opsonized sheep red blood cells (SRBC) by human monocyte-derived macrophages.
• To determine if HIV-1 infection affects complement-mediated phagocytosis.
• To establish a quantitative assay for studying phagocytosis in adherent macrophages.

Main Methods:

• Opsonization of SRBC with untreated or heat-inactivated human serum.
• Quantification of SRBC phagocytosis by human monocyte-derived macrophages using a colorimetric assay.
• Assessment of the role of complement receptors via inhibition studies with a protein kinase C (PKC)-specific inhibitor (RO 31-8220) and augmentation with phorbol ester (PMA).
• Evaluation of phagocytosis in macrophages infected with HIV-1.

Main Results:

• SRBC opsonized with untreated human serum were efficiently phagocytosed, with minimal lysis.
• Phagocytosis was mediated exclusively by complement receptors, as evidenced by the lack of uptake with heat-inactivated serum and augmentation by PMA.
• Inhibition of protein kinase C (PKC) significantly reduced phagocytosis.
• HIV-1 infection of macrophages markedly inhibited complement-mediated phagocytosis of SRBC.

Conclusions:

• Complement receptors are the primary mediators of SRBC phagocytosis by human monocyte-derived macrophages.
• HIV-1 infection impairs complement-mediated phagocytosis in these cells.
• The developed assay is a valuable tool for studying complement-mediated phagocytosis and its modulation by pathogens or pharmacological agents.