Surfactant protein A regulates IgG-mediated phagocytosis in inflammatory neutrophils

Abstract

Surfactant proteins (SP)-A and SP-D have been shown to affect the functions of a variety of innate immune cells and to interact with various immune proteins such as complement and immunoglobulins. The goal of the current study is to test the hypothesis that SP-A regulates IgG-mediated phagocytosis by neutrophils, which are major effector cells of the innate immune response that remove invading pathogens by phagocytosis and by extracellular killing mediated by reactive oxygen and nitrogen. We have previously shown that SP-A stimulates chemotaxis by inflammatory, but not peripheral, neutrophils. To evaluate the ability of SP-A to modulate IgG-mediated phagocytosis, polystyrene beads were coated with BSA and treated with anti-BSA IgG. SP-A significantly and specifically enhanced IgG-mediated phagocytosis by inflammatory neutrophils, but it had no effect on beads not treated with IgG. SP-A bound to IgG-coated beads and enhanced their uptake via direct interactions with the beads as well as direct interactions with the neutrophils. SP-A did not affect reactive oxygen production or binding of IgG to neutrophils and had modest effects on polymerization of actin. These data suggest that SP-A plays an important role in mediating the phagocytic response of neutrophils to IgG-opsonized particles.

Neutrophil-Mediated Phagocytosis of Staphylococcus aureus

“…Sp-A enhances the uptake of IgG-coated polystyrene beads by inflammatory neutrophils via direct interaction with both the opsonized beads and the neutrophils. In this case, the rat neutrophils were obtained from a lavage of LPS challenged lungs, and here SP-A did not have a generalized activation effect on neutrophils (70). …”

“…Activating agents have direct effects on cell surface receptor expression, but also intracellular in superoxide anion generation, degranulation, and mediator release (70). In the primed state, there is no increase in oxidase activity, yet subsequent stimulation provokes a response that is larger than in non-primed, activated cells.…”

Eosinophil-Associated Lung Diseases. A Cry for Surfactant Proteins A and D Help?

“…SP-A has been shown to enhance phagocytosis of IgG-opsonized particles (23) and complement-coated particles (24) and to preferentially bind apoptotic neutrophils, which aides in their removal from the inflamed lung (25,26). SP-D is known to aggregate and aid in the removal of pollen starch granules (27,28), to bind and enhance clearance of genomic DNA and apoptotic cells (29), and to aggregate and remove nanoparticles (30).…”

Inhibitory Effects of Areca Nut Extract on Expression of Complement Receptors and Fc Receptors in Human Neutrophils

“…To prepare the IgG‐opsonized microspheres, fluorescent microspheres were coated with IgG as described previously with modifications 27,28 . Briefly, microspheres were incubated with 10 mg/mL bovine serum albumin (BSA) ## in PBS for 1 hour at 37°C.…”