Autophagy Mediates Interleukin-1β Secretion in Human Neutrophils

Area of Science:

• Immunology
• Cell Biology
• Molecular Biology

Background:

• Interleukin-1β (IL-1β) is a key pro-inflammatory cytokine.
• Its secretion mechanism is unconventional, bypassing the classical ER-Golgi pathway.
• Neutrophils are crucial in infection and are significant sources of IL-1β.

Purpose of the Study:

• To investigate the role of secretory autophagy in IL-1β export from neutrophils.
• To elucidate the unconventional secretion pathway of IL-1β in neutrophils.

Main Methods:

• Inhibition of autophagy using 3-methyladenine, Wortmannin, Bafilomycin A1, E64d, and VPS34IN-1.
• siRNA-mediated knockdown of ATG5.
• Confocal microscopy to assess colocalization of IL-1β with LC3B and elastase.
• ELISA to quantify IL-1β and pro-IL-1β release.
• Cell starvation to stimulate autophagy.

Main Results:

• Autophagy inhibition significantly reduced LPS+ATP-induced IL-1β secretion without affecting neutrophil viability.
• IL-1β colocalized with LC3B in an autophagic compartment upon stimulation, preceding supernatant release.
• Autophagy stimulation via starvation enhanced IL-1β and LC3B colocalization and promoted IL-1β secretion.
• Serine protease inhibitors and elastase colocalization suggest involvement of granule contents in IL-1β secretion.

Conclusions:

• An unconventional autophagy-mediated secretory pathway is responsible for IL-1β secretion in human neutrophils.
• This pathway represents a novel mechanism for releasing leaderless inflammatory cytokines.
• Autophagy regulates the release of mature IL-1β, distinct from pro-IL-1β.