Rac2 regulates immune complex-mediated granule polarization and exocytosis in neutrophils

Area of Science:

• Immunology
• Cell Biology
• Molecular Biology

Background:

• Rac2 guanosine triphosphatase is vital for neutrophil degranulation.
• Rac2 knockout neutrophils show impaired primary granule release with certain stimuli.
• The role of Rac2 in degranulation using immune complexes and coronin 1A's involvement is unclear.

Purpose of the Study:

• To investigate Rac2's role in neutrophil degranulation and actin cytoskeleton rearrangement.
• To examine the relationship between Rac2, coronin 1A, and granule release upon immune complex stimulation.
• To determine the localization of Rac2 and coronin 1A in activated human neutrophils.

Main Methods:

• Utilized bone marrow neutrophils from wild-type and Rac2 knockout mice.
• Stimulated neutrophils with immobilized immune complexes.
• Assessed secretion of primary (myeloperoxidase), secondary (lactoferrin), and tertiary granule (MMP-2, MMP-9) products.
• Analyzed subcellular colocalization of coronin 1A, actin, and CD63 using deconvolution microscopy.

Main Results:

• Rac2 knockout neutrophils exhibited significantly altered release of myeloperoxidase, MMP-2, and MMP-9, but not lactoferrin.
• Immune complex stimulation led to reduced filopodia formation and CD63 polarization in Rac2 knockout neutrophils.
• Coronin 1A colocalization with CD63 was diminished in Rac2 knockout neutrophils.
• Rac2 and coronin 1A were observed associated with granules in activated human neutrophils.

Conclusions:

• Rac2 plays a significant role in neutrophil degranulation stimulated by immune complexes.
• Rac2 facilitates the polarization of CD63+ granules to the cell surface, dependent on coronin 1A.
• Rac2 is involved in Rac2-mediated regulation of granule exocytosis and filopodia formation.