Neutrophil-Mediated Phagocytosis of Staphylococcus aureus

Abstract

Initial elimination of invading Staphylococcus aureus from the body is mediated by professional phagocytes. The neutrophil is the major phagocyte of the innate immunity and plays a key role in the host defense against staphylococcal infections. Opsonization of the bacteria with immunoglobulins and complement factors enables efficient recognition by the neutrophil that subsequently leads to intracellular compartmentalization and killing. Here, we provide a review of the key processes evolved in neutrophil-mediated phagocytosis of S. aureus and briefly describe killing. As S. aureus is not helpless against the professional phagocytes, we will also highlight its immune evasion arsenal related to phagocytosis.

Keywords: Staphylococcus aureus; neutrophil; phagocytosis.

Figure 1

Interface neutrophil and S. aureus. Several groups of receptors mediate neutrophils recognition of S. aureus upon opsonization and others are involved in activation or priming of phagocytosis. Targets on the S. aureus surface are the cell wall components peptidoglycan (PG), wall teichoic acid (WTA), lipoteichoic acid (LTA), capsule (“gray area”), and representative associated proteins clumping factor A (ClfA) and protein-A (Spa). Targets are decorated with serum derived opsonins IgG (binding with their Fab part) and C3b. Note the reverse Fc-dependent association of IgG with Spa. Receptors on the neutrophil surface involved in recognition of the opsonized S. aureus are FcγRII and FcγRIII for IgG, and CR1 and CR3 for C3b (and iC3b). Examples of receptors on the neutrophil involved in priming or activation of phagocytosis are complement receptors C3aR for C3a and C5aR for C5a, CXCR1 for il-8, and TNFR for TNFα. The heterodimer TLR2/TLR6 represents a common pattern recognition receptor for bacterial lipoproteins.

Figure 2

Neutrophil phagocytosis of S. aureus. (A) Upon recognition of opsonized S. aureus, neutrophils internalize the bacterium in a phagosome where secretory granule content is released and ROS are produced that mediate killing of the bacterium. (B) Confocal microscopy image of S. aureus expressing green fluorescence protein (green) attached (left) to and phagocytosed (right) by neutrophils [red, membrane stain wheat germ agglutinin (WGA)-Alexa647, blue, nucleic acid stain Syto82].