Caspase-1 and Caspase-11 Mediate Pyroptosis, Inflammation, and Control of Brucella Joint Infection

Abstract

Brucellosis, caused by the intracellular bacterial pathogen <i>Brucella</i>, is a zoonotic disease for which arthritis is the most common focal complication in humans. Here we investigated the role of inflammasomes and their effectors, including interleukin-1 (IL-1), IL-18, and pyroptosis, on inflammation and control of infection during <i>Brucella</i>-induced arthritis. Early in infection, both caspase-1 and caspase-11 were found to initiate joint inflammation and proinflammatory cytokine production. However, by 1 week postinfection, caspase-1 and caspase-11 also contributed to control of <i>Brucella</i> joint infection. Inflammasome-dependent restriction of <i>Brucella</i> joint burdens did not require AIM2 (absent in melanoma 2) or NLRP3 (NLR family, pyrin domain containing 3). IL-1R had a modest effect on <i>Brucella</i>-induced joint swelling, but mice lacking IL-1R were not impaired in their ability to control infection of the joint by <i>Brucella</i> In contrast, IL-18 contributed to the initiation of joint swelling and control of joint <i>Brucella</i> infection. Caspase1/11-dependent cell death was observed <i>in vivo</i>, and <i>in vitro</i> studies demonstrated that both caspase-1 and caspase-11 induce pyroptosis, which limited <i>Brucella</i> infection in macrophages. <i>Brucella</i> lipopolysaccharide alone was also able to induce caspase-11-dependent pyroptosis. Collectively, these data demonstrate that inflammasomes induce inflammation in an IL-18-dependent manner and that inflammasome-dependent IL-18 and pyroptosis restrict <i>Brucella</i> infection.