Fulton S A, Johnsen J M, Wolf S F, Sieburth D S, Boom W H
Division of Infectious Diseases, Department of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4984, USA.
Infect Immun. 1996 Jul;64(7):2523-31. doi: 10.1128/iai.64.7.2523-2531.1996.
Mycobacterium tuberculosis and its antigens are potent inducers of cytokine expression by mononuclear phagocytes. In this study, the ability of live M. tuberculosis to stimulate interleukin-12 (IL-12) expression by human monocytes was examined. Monocytes were purified from peripheral blood mononuclear cells by adherence and either infected with M. tuberculosis or exposed to soluble protein antigens of M. tuberculosis (purified protein derivative [PPD]). Live M. tuberculosis (10(6) to 10(7) CFU/ml) was a potent stimulus for interleukin-12 (IL-12). By using reverse transcription-PCR, p40 mRNA was detected at 3 h, peaked at 6 to 12 h, and decayed to baseline levels at 18 to 24 h following infection. Bioactive IL-12 (p70) was measured by the phytohemagglutinin blast proliferation assay and confirmed the p40 mRNA results. In contrast, soluble PPD at concentrations known to readily induce IL-1 and tumor necrosis factor alpha expression by monocytes (10 to 100 microg/ml) was a poor stimulus for IL-12 p40 mRNA expression. The different efficiencies of M. tuberculosis bacilli and PPD for IL-12 expression by monocytes was in part due to a requirement for phagocytosis. Induction of IL-12 in response to M. tuberculosis was reduced by cytochalasin D. Furthermore, phagocytosis of dead M. tuberculosis or inert 2-micron-diameter polystyrene beads by monocytes induced IL-12 p40 mRNA. In contrast, 0.5-micron-diameter beads, which can enter cells through pinocytosis, did not stimulate IL-12 expression. Functionally, IL-12 readily enhanced PPD-stimulated IFN-gamma production and CD4+ T-cell-mediated cytotoxicity by peripheral blood mononuclear cells from healthy tuberculin-positive donors but induced less enhancement when live M. tuberculosis was the antigen. These results suggest that IL-12 is upregulated as part of the early cytokine response of mononuclear phagocytes to M. tuberculosis and that the cellular events associated with phagocytosis are themselves a potent signal for IL-12 production. IL-12 released by infected macrophages in turn can further upregulate M. tuberculosis-specific CD4+ T-cell effector function.
结核分枝杆菌及其抗原是单核吞噬细胞细胞因子表达的有效诱导剂。在本研究中，检测了活的结核分枝杆菌刺激人单核细胞表达白细胞介素-12（IL-12）的能力。通过贴壁从外周血单核细胞中纯化单核细胞，然后用结核分枝杆菌感染或使其暴露于结核分枝杆菌的可溶性蛋白抗原（纯化蛋白衍生物[PPD]）。活的结核分枝杆菌（10⁶至10⁷CFU/ml）是白细胞介素-12（IL-12）的有效刺激物。通过逆转录聚合酶链反应，在感染后3小时检测到p40 mRNA，在6至12小时达到峰值，并在18至24小时衰减至基线水平。通过植物血凝素刺激的增殖试验测量生物活性IL-12（p70），并证实了p40 mRNA的结果。相比之下，已知浓度的可溶性PPD（10至100μg/ml）可轻易诱导单核细胞表达IL-1和肿瘤坏死因子α，但对IL-12 p40 mRNA表达的刺激作用较弱。结核分枝杆菌杆菌和PPD对单核细胞IL-12表达的不同效率部分归因于吞噬作用的需求。细胞松弛素D可降低对结核分枝杆菌的反应中IL-12的诱导。此外，单核细胞吞噬死亡的结核分枝杆菌或惰性的2微米直径聚苯乙烯珠可诱导IL-12 p40 mRNA。相比之下，可通过胞饮作用进入细胞的0.5微米直径的珠子不会刺激IL-12表达。在功能上，IL-12可轻易增强PPD刺激的健康结核菌素阳性供体外周血单核细胞产生的IFN-γ以及CD4⁺T细胞介导的细胞毒性，但当以活的结核分枝杆菌为抗原时，诱导的增强作用较小。这些结果表明，IL-12作为单核吞噬细胞对结核分枝杆菌早期细胞因子反应的一部分被上调，并且与吞噬作用相关的细胞事件本身就是IL-12产生的有效信号。被感染的巨噬细胞释放的IL-12反过来可进一步上调结核分枝杆菌特异性CD4⁺T细胞效应功能。
