Appelmelk B J, den Dunnen J, Driessen N N, Ummels R, Pak M, Nigou J, Larrouy-Maumus G, Gurcha S S, Movahedzadeh F, Geurtsen J, Brown E J, Eysink Smeets M M, Besra G S, Willemsen P T J, Lowary T L, van Kooyk Y, Maaskant J J, Stoker N G, van der Ley P, Puzo G, Vandenbroucke-Grauls C M J E, Wieland C W, van der Poll T, Geijtenbeek T B H, van der Sar A M, Bitter W
Department of Medical Microbiology and Infection Control, VU University Medical Center, 1081 BT Amsterdam, The Netherlands.
Cell Microbiol. 2008 Apr;10(4):930-44. doi: 10.1111/j.1462-5822.2007.01097.x. Epub 2007 Dec 5.
Pathogenic mycobacteria have the ability to persist in phagocytic cells and to suppress the immune system. The glycolipid lipoarabinomannan (LAM), in particular its mannose cap, has been shown to inhibit phagolysosome fusion and to induce immunosuppressive IL-10 production via interaction with the mannose receptor or DC-SIGN. Hence, the current paradigm is that the mannose cap of LAM is a crucial factor in mycobacterial virulence. However, the above studies were performed with purified LAM, never with live bacteria. Here we evaluate the biological properties of capless mutants of Mycobacterium marinum and M. bovis BCG, made by inactivating homologues of Rv1635c. We show that its gene product is an undecaprenyl phosphomannose-dependent mannosyltransferase. Compared with parent strain, capless M. marinum induced slightly less uptake by and slightly more phagolysosome fusion in infected macrophages but this did not lead to decreased survival of the bacteria in vitro, nor in vivo in zebra fish. Loss of caps in M. bovis BCG resulted in a sometimes decreased binding to human dendritic cells or DC-SIGN-transfected Raji cells, but no differences in IL-10 induction were observed. In mice, capless M. bovis BCG did not survive less well in lung, spleen or liver and induced a similar cytokine profile. Our data contradict the current paradigm and demonstrate that mannose-capped LAM does not dominate the Mycobacterium-host interaction.
致病性分枝杆菌能够在吞噬细胞中持续存在并抑制免疫系统。糖脂脂阿拉伯甘露聚糖（LAM），尤其是其甘露糖帽，已被证明可抑制吞噬溶酶体融合，并通过与甘露糖受体或DC-SIGN相互作用诱导免疫抑制性IL-10的产生。因此，目前的观点是LAM的甘露糖帽是分枝杆菌毒力的关键因素。然而，上述研究是用纯化的LAM进行的，从未用活细菌进行过。在这里，我们评估了通过使Rv1635c的同源物失活而构建的海分枝杆菌和牛分枝杆菌卡介苗无帽突变体的生物学特性。我们表明其基因产物是一种十一异戊烯基磷酸甘露糖依赖性甘露糖基转移酶。与亲本菌株相比，无帽的海分枝杆菌在感染的巨噬细胞中诱导的摄取略少，吞噬溶酶体融合略多，但这并未导致细菌在体外或斑马鱼体内的存活率降低。牛分枝杆菌卡介苗中帽的缺失有时会导致与人树突状细胞或DC-SIGN转染的Raji细胞的结合减少，但未观察到IL-10诱导的差异。在小鼠中，无帽的牛分枝杆菌卡介苗在肺、脾或肝中的存活情况并未变差，且诱导的细胞因子谱相似。我们的数据与当前的观点相矛盾，并表明带甘露糖帽的LAM并不主导分枝杆菌与宿主的相互作用。
