Neutrophils Require Activation to Express Functional Cell-Surface Complement Receptor Immunoglobulin.

Area of Science:

• Immunology
• Cell Biology

Background:

• Complement Receptor Immunoglobulin (CRIg) is primarily expressed on macrophages and promotes phagocytosis.
• Its expression can be modulated by inflammatory mediators, suggesting potential roles in other phagocytes.

Purpose of the Study:

• To investigate whether neutrophils express CRIg and if its expression is regulated by inflammatory mediators.
• To determine the functional consequences of CRIg expression on neutrophils.

Main Methods:

• Western blot and RT-PCR to detect CRIg expression in neutrophils.
• Flow cytometry to quantify cell surface and intracellular CRIg levels.
• Stimulation of neutrophils with various inflammatory mediators and activators.
• Assessment of CRIg-mediated neutrophil functions, including superoxide release, MAP kinase activation, bacterial killing, and neutrophil extracellular trap formation.

Main Results:

• Resting neutrophils express a 35 kDa CRIg isoform, detectable by Western blot and RT-PCR.
• CRIg is primarily intracellular but significantly increases on the neutrophil surface upon activation with inflammatory mediators (e.g., TNF, GM-CSF, LPS).
• Upregulation of CRIg requires p38 MAP kinase, protein kinase C, intracellular calcium, actin cytoskeleton, and exocytosis.
• Engagement of CRIg enhances neutrophil superoxide release, p38 activation, and Staphylococcus aureus killing, while GM-CSF priming induces neutrophil extracellular trap release.
• The anti-inflammatory cytokine IL-10 decreased basal and GM-CSF-induced CRIg expression.

Conclusions:

• Neutrophils express and upregulate CRIg in response to inflammatory signals.
• Neutrophil CRIg plays a crucial role in antimicrobial defense, requiring priming for optimal function.
• CRIg represents a potential therapeutic target for modulating neutrophil-mediated immune responses.