Marshall N E, Ziegler H K
Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, GA 30322.
J Immunol. 1991 Oct 1;147(7):2324-32.
The production of a hemolytic exotoxin (Hly) termed listeriolysin O (LLO) is a major determinant of the virulence of the Gram-positive bacterium Listeria monocytogenes. As determined by lethal inoculum size, LLO- strains of L. monocytogenes generally are several orders of magnitude less virulent than their LLO+ counterparts. The generation of protective anti-Listeria T cell immunity also has been shown to depend on the LLO phenotype of the bacteria present during primary infection, although the cellular basis of this observation is not known. The experiments described here address the role of LLO in regulation of the expression of class II MHC (Ia) molecules by murine macrophages. Because Ia expression by macrophages and other APC is thought to be a central factor in the generation of T cells specific for bacterial Ag, we have tested the hypothesis that the failure of LLO- strains to elicit anti-Listeria T cell responses might be secondary to an inability of these strains to stimulate increases in macrophage Ia levels. Our results show that the macrophage Ia response after i.p. injection of L. monocytogenes correlates strongly with the LLO phenotype of the bacteria. The presence of LLO+ organisms, even at very small numbers (as few as 10), elicits a striking increase in Ia expression by peritoneal macrophages. In contrast, even at very high numbers (up to 10(6) per mouse), LLO- bacteria fail to stimulate a strong Ia response. We also have analyzed macrophage Ia expression after injection of lysates of Escherichia coli expressing recombinant LLO protein. Similar to the results obtained with LLO+ and LLO- L. monocytogenes, we have observed Ia induction only with LLO+ lysates. Ia induction by this crude recombinant LLO preparation can be inhibited by cholesterol or heat. Furthermore, supernatants derived from cultures of LLO+ (but not LLO-) L. monocytogenes can cause Ia induction when administered via i.p. injection. Taken together, these findings suggest that the failure of macrophages to respond to LLO- organisms with an increase in Ia expression may be a major underlying cause of the failure of these bacteria to induce Listeria-specific protective T cell immunity. Furthermore, we propose that the induction of macrophage Ia expression in response to bacterial toxins such as Hly may represent one component of a set of early, innate immune mechanisms, and that this induction may provide a critical "bridge" to later, acquired, Ag-specific immune processes.
一种名为李斯特菌溶血素O（LLO）的溶血性外毒素的产生是革兰氏阳性菌单核细胞增生李斯特菌毒力的主要决定因素。根据致死接种量测定，单核细胞增生李斯特菌的LLO-菌株的毒力通常比其LLO+对应菌株低几个数量级。保护性抗李斯特菌T细胞免疫的产生也已被证明取决于初次感染期间存在的细菌的LLO表型，尽管这一观察结果的细胞基础尚不清楚。此处描述的实验探讨了LLO在调节小鼠巨噬细胞II类主要组织相容性复合体（Ia）分子表达中的作用。由于巨噬细胞和其他抗原呈递细胞（APC）的Ia表达被认为是产生针对细菌抗原的T细胞的核心因素，我们检验了以下假设：LLO-菌株未能引发抗李斯特菌T细胞反应可能是由于这些菌株无法刺激巨噬细胞Ia水平升高所致。我们的结果表明，腹腔注射单核细胞增生李斯特菌后巨噬细胞的Ia反应与细菌的LLO表型密切相关。即使数量非常少（低至10个），LLO+菌的存在也会引起腹腔巨噬细胞Ia表达的显著增加。相反，即使数量非常多（每只小鼠高达10⁶个），LLO-菌也无法刺激强烈的Ia反应。我们还分析了注射表达重组LLO蛋白的大肠杆菌裂解物后巨噬细胞的Ia表达。与使用LLO+和LLO-单核细胞增生李斯特菌获得的结果类似，我们仅观察到LLO+裂解物能诱导Ia。这种粗制重组LLO制剂诱导Ia可被胆固醇或加热抑制。此外，LLO+（而非LLO-）单核细胞增生李斯特菌培养物的上清液经腹腔注射给药时可引起Ia诱导。综上所述，这些发现表明巨噬细胞对LLO-菌无Ia表达增加反应可能是这些细菌无法诱导李斯特菌特异性保护性T细胞免疫的主要潜在原因。此外，我们提出巨噬细胞对诸如Hly等细菌毒素的反应诱导Ia表达可能代表一组早期固有免疫机制的一个组成部分，并且这种诱导可能为后期获得性抗原特异性免疫过程提供关键的“桥梁”。
