Use of Flow Cytometry to Evaluate Phagocytosis of Staphylococcus aureus by Human Neutrophils

Abstract

Neutrophils play a key role in the human immune response to <i>Staphylococcus aureus</i> infections. These professional phagocytes rapidly migrate to the site of infection to engulf bacteria and destroy them <i>via</i> specialized intracellular killing mechanisms. Here we describe a robust and relatively high-throughput flow cytometry assay to quantify phagocytosis of <i>S. aureus</i> by human neutrophils. We show that effective phagocytic uptake of <i>S. aureus</i> is greatly enhanced by opsonization, i.e. the tagging of microbial surfaces with plasma-derived host proteins like antibodies and complement. Our rapid assay to monitor phagocytosis can be used to study neutrophil deficiencies and bacterial evasion, but also provides a powerful tool to assess the opsonic capacity of antibodies, either in the context of natural immune responses or immune therapies.