Skerrett S J, Martin T R
Medical Research Service, Veterans Affairs Medical Center, Seattle, Washington 98108, USA.
Infect Immun. 1996 Aug;64(8):3236-43. doi: 10.1128/iai.64.8.3236-3243.1996.
Legionella pneumophila is an intracellular parasite of alveolar macrophages, and recovery from legionellosis is associated with activation of alveolar macrophages to resist intracellular bacterial replication. Gamma interferon (IFN-gamma) is known to activate alveolar macrophages to suppress L. pneumophila, but the role of macrophage-derived cytokines in modulating alveolar macrophage resistance is unknown. To test the hypothesis that macrophage-derived mediators contribute to the resistance of alveolar macrophages to L. pneumophila, we incubated adherent rat alveolar macrophages with Escherichia coli lipopolysaccharide (LPS), recombinant tumor necrosis factor alpha (TNF-alpha), recombinant IFN-gamma, neutralizing anti-TNF-alpha, and/or N(G)-monomethyl-L-arginine (L-NMMA) for 6 h before challenge with L. pneumophila. Monolayers were sonically disrupted and quantitatively cultured on successive days. We also measured bioactive TNF-alpha release by infected macrophages in the presence or absence of IFN-gamma. We found that pretreatment of alveolar macrophages with LPS or, to a lesser degree, TNF-alpha, significantly inhibited intracellular replication of L. pneumophila. Both LPS and TNF-alpha acted synergistically with IFN-gamma at less than the maximally activating concentration to suppress L. pneumophila growth. The independent and coactivating effects of LPS were blocked by anti-TNF-alpha. Killing of L. pneumophila by IFN-gamma at the maximally activating concentration was inhibited by anti-TNF-alpha. The synergistic effects of TNF-alpha. or LPS in combination with IFN-gamma were inhibited by L-NMMA. Infected alveolar macrophages secreted TNF-alpha in proportion to the bacterial inoculum, and secretion of TNF-alpha was potentiated by cocultivation with IFN-gamma. These data indicate that secretion of TNF-alpha is an important autocrine defense mechanism of alveolar macrophages, serving to potentiate the activating effects of IFN-gamma through costimulation of nitric oxide synthesis.
嗜肺军团菌是肺泡巨噬细胞的细胞内寄生虫，从军团病中恢复与肺泡巨噬细胞激活以抵抗细胞内细菌复制有关。已知γ干扰素（IFN-γ）可激活肺泡巨噬细胞以抑制嗜肺军团菌，但巨噬细胞衍生的细胞因子在调节肺泡巨噬细胞抗性中的作用尚不清楚。为了检验巨噬细胞衍生介质有助于肺泡巨噬细胞抵抗嗜肺军团菌这一假说，在用嗜肺军团菌攻击前6小时，我们将贴壁的大鼠肺泡巨噬细胞与大肠杆菌脂多糖（LPS）、重组肿瘤坏死因子α（TNF-α）、重组IFN-γ、中和性抗TNF-α和/或N（G）-单甲基-L-精氨酸（L-NMMA）一起孵育。单层细胞经超声破碎后连续几天进行定量培养。我们还测量了在有或没有IFN-γ存在的情况下感染巨噬细胞释放的生物活性TNF-α。我们发现，用LPS或程度较轻的TNF-α预处理肺泡巨噬细胞，可显著抑制嗜肺军团菌的细胞内复制。LPS和TNF-α在低于最大激活浓度时均与IFN-γ协同作用以抑制嗜肺军团菌生长。LPS的独立激活作用和协同激活作用均被抗TNF-α阻断。在最大激活浓度下，IFN-γ对嗜肺军团菌的杀伤作用被抗TNF-α抑制。TNF-α或LPS与IFN-γ联合的协同作用被L-NMMA抑制。感染的肺泡巨噬细胞分泌的TNF-α与细菌接种量成比例，并且与IFN-γ共培养可增强TNF-α的分泌。这些数据表明，TNF-α的分泌是肺泡巨噬细胞重要的自分泌防御机制，通过共刺激一氧化氮合成来增强IFN-γ的激活作用。
