Cieniewicz Brandon, Dong Qiwen, Li Gang, Forrest James C, Mounce Bryan C, Tarakanova Vera L, van der Velden Adrianus, Krug Laurie T
Department of Molecular Genetics and Microbiology, Stony Brook University, Stony Brook, New York, USA Molecular and Cellular Biology Program, Stony Brook University, Stony Brook, New York, USA.
Department of Microbiology and Immunology, University of Arkansas for Medical Sciences, Little Rock, Arkansas, USA.
J Virol. 2015 Jul;89(13):6562-74. doi: 10.1128/JVI.00658-15. Epub 2015 Apr 8.
Gammaherpesviruses establish lifelong infections that are associated with the development of cancer. These viruses subvert many aspects of the innate and adaptive immune response of the host. The inflammasome, a macromolecular protein complex that controls inflammatory responses to intracellular danger signals generated by pathogens, is both activated and subverted during human gammaherpesvirus infection in culture. The impact of the inflammasome response on gammaherpesvirus replication and latency in vivo is not known. Caspase-1 is the inflammasome effector protease that cleaves the proinflammatory cytokines interleukin-1β (IL-1β) and IL-18. We infected caspase-1-deficient mice with murine gammaherpesvirus 68 (MHV68) and observed no impact on acute replication in the lung or latency and reactivation from latency in the spleen. This led us to examine the effect of viral infection on inflammasome responses in bone marrow-derived macrophages. We determined that infection of macrophages with MHV68 led to a robust interferon response but failed to activate caspase-1 or induce the secretion of IL-1β. In addition, MHV68 infection led to a reduction in IL-1β production after extrinsic lipopolysaccharide stimulation or upon coinfection with Salmonella enterica serovar Typhimurium. Interestingly, this impairment occurred at the proIL-1β transcript level and was independent of the RTA, the viral lytic replication and transcription activator. Taken together, MHV68 impairs the inflammasome response by inhibiting IL-1β production during the initial stages of infection.
Gammaherpesviruses persist for the lifetime of the host. To accomplish this, they must evade recognition and clearance by the immune system. The inflammasome consists of proteins that detect foreign molecules in the cell and respond by secreting proinflammatory signaling proteins that recruit immune cells to clear the infection. Unexpectedly, we found that murine gammaherpesvirus pathogenesis was not enhanced in mice lacking caspase-1, a critical inflammasome component. This led us to investigate whether the virus actively impairs the inflammasome response. We found that the inflammasome was not activated upon macrophage cell infection with murine gammaherpesvirus 68. Infection also prevented the host cell inflammasome response to other pathogen-associated molecular patterns, indicated by reduced production of the proinflammatory cytokine IL-1β upon bacterial coinfection. Taken together, murine gammaherpesvirus impairment of the inflammatory cytokine IL-1β in macrophages identifies one mechanism by which the virus may inhibit caspase-1-dependent immune responses in the infected animal.
γ疱疹病毒可建立终身感染，且与癌症的发生有关。这些病毒会破坏宿主先天和适应性免疫反应的多个方面。炎性小体是一种大分子蛋白质复合物，可控制对病原体产生的细胞内危险信号的炎症反应，在培养的人γ疱疹病毒感染过程中，它既会被激活，也会被破坏。炎性小体反应对γ疱疹病毒在体内复制和潜伏的影响尚不清楚。半胱天冬酶-1是炎性小体效应蛋白酶，可切割促炎细胞因子白细胞介素-1β（IL-1β）和IL-18。我们用鼠γ疱疹病毒68（MHV68）感染半胱天冬酶-1缺陷小鼠，发现对肺部的急性复制或脾脏中的潜伏及潜伏再激活均无影响。这促使我们研究病毒感染对骨髓来源巨噬细胞中炎性小体反应的影响。我们确定，用MHV68感染巨噬细胞会引发强烈的干扰素反应，但无法激活半胱天冬酶-1或诱导IL-1β的分泌。此外，MHV68感染会导致在外部脂多糖刺激后或与鼠伤寒沙门氏菌共感染时IL-1β产生减少。有趣的是，这种损伤发生在proIL-1β转录水平，且独立于病毒裂解复制和转录激活因子RTA。综上所述，MHV68在感染初期通过抑制IL-1β的产生来损害炎性小体反应。
γ疱疹病毒在宿主的一生中持续存在。为实现这一点，它们必须逃避免疫系统的识别和清除。炎性小体由检测细胞内异物分子的蛋白质组成，并通过分泌促炎信号蛋白来做出反应，这些蛋白会募集免疫细胞以清除感染。出乎意料的是，我们发现缺乏关键炎性小体成分半胱天冬酶-1的小鼠中，鼠γ疱疹病毒的发病机制并未增强。这促使我们研究该病毒是否会主动损害炎性小体反应。我们发现，用鼠γ疱疹病毒68感染巨噬细胞后，炎性小体未被激活。感染还会阻止宿主细胞炎性小体对其他病原体相关分子模式的反应，这表现为细菌共感染时促炎细胞因子IL-1β的产生减少。综上所述，鼠γ疱疹病毒对巨噬细胞中炎性细胞因子IL-1β的损害确定了该病毒在受感染动物中抑制半胱天冬酶-1依赖性免疫反应的一种机制。
