期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2022
卷号：119
期号：2
DOI：10.1073/pnas.2116415119
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Significance
Anthrax is a deadly infection caused by exposure to
Bacillus anthracis bacteria. Anthrax lethal toxin (LeTx) has long been recognized as a major determinant of lethal anthrax, which paralyzes the host’s immune defenses by killing off macrophages. Despite the importance of macrophage cytotoxicity in anthrax pathogenesis, the signaling pathways underlying cell death of
B. anthracis-infected macrophages are poorly understood. This study shows that infection with live
B. anthracis or LeTx intoxication sensitizes macrophages to TNF-dependent NLRP3 inflammasome activation and caspase-8–mediated apoptosis. Moreover, caspase-8–mediated apoptosis is shown to promote anthrax-associated lethality in vivo. Collectively, the study establishes TNF- and RIPK1 kinase activity–dependent NLRP3 inflammasome activation and macrophage apoptosis as key host–pathogen mechanisms in lethal anthrax.
Lethal toxin (LeTx)-mediated killing of myeloid cells is essential for
Bacillus anthracis, the causative agent of anthrax, to establish systemic infection and induce lethal anthrax. The “LeTx-sensitive” NLRP1b inflammasome of BALB/c and 129S macrophages swiftly responds to LeTx intoxication with pyroptosis and secretion of interleukin (IL)-1β. However, human NLRP1 is nonresponsive to LeTx, prompting us to investigate
B. anthracis host–pathogen interactions in C57BL/6J (B6) macrophages and mice that also lack a LeTx-sensitive
Nlrp1b allele. Unexpectedly, we found that LeTx intoxication and live
B. anthracis infection of B6 macrophages elicited robust secretion of IL-1β, which critically relied on the NLRP3 inflammasome. TNF signaling through both TNF receptor 1 (TNF-R1) and TNF-R2 were required for
B. anthracis-induced NLRP3 inflammasome activation, which was further controlled by RIPK1 kinase activity and LeTx-mediated proteolytic inactivation of MAP kinase signaling. In addition to activating the NLRP3 inflammasome, LeTx-induced MAPKK inactivation and TNF production sensitized
B. anthracis-infected macrophages to robust RIPK1- and caspase-8–dependent apoptosis. In agreement, purified LeTx triggered RIPK1 kinase activity- and caspase-8–dependent apoptosis only in macrophages primed with TNF or following engagement of TRIF-dependent Toll-like receptors. Consistently, genetic and pharmacological inhibition of RIPK1 inhibited NLRP3 inflammasome activation and apoptosis of LeTx-intoxicated and
B. anthracis-infected macrophages. Caspase-8/RIPK3-deficient mice were significantly protected from
B. anthracis-induced lethality, demonstrating the in vivo pathophysiological relevance of this cytotoxic mechanism. Collectively, these results establish TNF- and RIPK1 kinase activity–dependent NLRP3 inflammasome activation and macrophage apoptosis as key host–pathogen mechanisms in lethal anthrax.
