Aggregates are the biologically active units of endotoxin
Aggregates are the biologically active units of endotoxin
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DOI：
10.1074/jbc.m401231200
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发表时间：
2004-06-18
影响因子：
4.8
通讯作者：
Seydel, U
中科院分区：
文献类型：
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作者：
Mueller, M;Lindner, B;Seydel, U
为了阐明内毒素（脂多糖，LPS）激活免疫细胞导致促炎细胞因子产生和释放的早期步骤，必须解决有关内毒素生物活性单位的问题：单体内毒素分子是否能够激活细胞，或者活性单位是否由较大的内毒素聚集体代表？这个问题在过去一直有争议。受以下观察的启发，即来自大肠杆菌的脂质A（具有其内毒素原理的LPS的脂质部分）的天然分离物比相同量的合成大肠杆菌表达更高的内毒素活性。大肠杆菌样六酰化脂质A（化合物506），我们仔细研究了天然分离物的化学组成。我们发现在这些分离株中，最大的部分是六酰化的，但也存在大量的五酰化和四酰化分子，当将其施用于人单核细胞时，可能会拮抗具有生物活性的六酰化内毒素对细胞因子的诱导。我们制备了以不同摩尔比混合的化合物506或406（四酰化前体IVa）的单独聚集体，以及含有相同比例的两种化合物的混合聚集体。令人惊讶的是，后一种混合物显示出比纯化合物506更高的内毒素活性，直到20%的化合物406的混合物。当使用各种磷脂代替化合物406时，获得了类似的结果。这些观察结果只能通过假设内毒素的活性单位是聚集体来理解。我们通过透析程序制备单体脂质A和LPS进一步证实了这一结果，并发现在相同浓度下，只有聚集体具有生物活性，而单体没有显示出活性。
For the elucidation of the very early steps of immune cell activation by endotoxins (lipopolysaccharide, LPS) leading to the production and release of proinflammatory cytokines the question concerning the biologically active unit of endotoxins has to be addressed: are monomeric endotoxin molecules able to activate cells or is the active unit represented by larger endotoxin aggregates? This question has been answered controversially in the past. Inspired by the observation that natural isolates of lipid A, the lipid moiety of LPS harboring its endotoxic principle, from Escherichia coli express a higher endotoxic activity than the same amounts of the synthetic E. coli-like hexaacylated lipid A (compound 506), we looked closer at the chemical composition of natural isolates. We found in these isolates that the largest fraction was hexaacylated, but also significant amounts of penta- and tetraacylated molecules were present that, when administered to human mononuclear cells, may antagonize the induction of cytokines by biologically active hexaacylated endotoxins. We prepared separate aggregates of either compound 506 or 406 (tetraacylated precursor IVa), mixed at different molar ratios, and mixed aggregates containing both compounds in the same ratios. Surprisingly, the latter mixtures showed higher endotoxic activity than that of the pure compound 506 up to an admixture of 20% of compound 406. Similar results were obtained when using various phospholipids instead of compound 406. These observations can only be understood by assuming that the active unit of endotoxins is the aggregate. We further confirmed this result by preparing monomeric lipid A and LPS by a dialysis procedure and found that, at the same concentrations, only the aggregates were biologically active, whereas the monomers showed no activity.