MINFLUX-nanoscopy of hNAIP/NLRC4 inflammasome activation in single human macrophages

Researchers employed super-resolution imaging technology, such as MINFLUX nanoscopy, to delve into the intricate cellular processes underlying the activation of the NAIP/NLRC4 inflammasome in human macrophages. This investigation focused on the phagocytosis of Yersinia enterocolitica, a specific strain of bacteria that harbors a type III secretion system (T3SS).

Upon the phagosome disruption caused by T3SS, the human NAIP (hNAIP) protein, which detects T3SS components and subsequently activates NLRC4, was gathered around bacteria-containing phagosomes.

The accumulation of NLRC4, NLRP3, and the adapter protein ASC in a dense condensate called a speck was triggered by the disruption of a single phagosome within a macrophage. Over time, inflammasome clusters containing NLRC4 and NLRP3/NLRC4 increasingly incorporated ASC, forming specks. Employing MINFLUX-nanoscopy, scientists were able to visually identify hNAIP at disrupted phagosomes with nanometer precision, revealing critical insights into the organization and number of NLRC4 inflammasome discs within a speck, as well as their hNAIP content.

The surprising revelation was the significant variation in the number of NLRC4 inflammasome discs, ranging from 35 to 249 per speck. Moreover, only a small fraction of these discs contained hNAIP. These findings substantially enhance our understanding of the activation mechanism of the hNAIP/NLRC4 inflammasome in macrophages ingesting bacteria equipped with a T3SS.