Brandt S, Krauel K, Gottschalk K E, Renné T, Helm C A, Greinacher A, Block S
Prof. Dr. med. Andreas Greinacher, Institut für Immunologie und Transfusionsmedizin, Sauerbruchstrasse, 17475 Greifswald, Germany, Tel.: +49 3834 865482, Fax: +49 3834 865489, E-mail:
Stephan Block, PhD, Applied Physics, Chalmers University of Technology, Fysikgränd 3, S-412 96 Gothenburg, Sweden, E-mail:
Thromb Haemost. 2014 Jul 3;112(1):53-64. doi: 10.1160/TH13-08-0634. Epub 2014 Mar 27.
Heparin-induced thrombocytopenia (HIT) is the most frequent drug-induced immune reaction affecting blood cells. Its antigen is formed when the chemokine platelet factor 4 (PF4) complexes with polyanions. By assessing polyanions of varying length and degree of sulfation using immunoassay and circular dichroism (CD)-spectroscopy, we show that PF4 structural changes resulting in antiparallel β-sheet content >30% make PF4/polyanion complexes antigenic. Further, we found that polyphosphates (polyP-55) induce antigenic changes on PF4, whereas fondaparinux does not. We provide a model suggesting that conformational changes exposing antigens on PF4/polyanion complexes occur in the hairpin involving AA 32-38, which form together with C-terminal AA (66-70) of the adjacent PF4 monomer a continuous patch on the PF4 tetramer surface, explaining why only tetrameric PF4 molecules express "HIT antigens". The correlation of antibody binding in immunoassays with PF4 structural changes provides the intriguing possibility that CD-spectroscopy could become the first antibody-independent, in vitro method to predict potential immunogenicity of drugs. CD-spectroscopy could identify compounds during preclinical drug development that induce PF4 structural changes correlated with antigenicity. The clinical relevance can then be specifically addressed during clinical trials. Whether these findings can be transferred to other endogenous proteins requires further studies.
肝素诱导的血小板减少症（HIT）是影响血细胞的最常见药物诱导的免疫反应。当趋化因子血小板因子4（PF4）与多阴离子结合时，其抗原就会形成。通过使用免疫测定和圆二色性（CD）光谱评估不同长度和硫酸化程度的多阴离子，我们发现导致反平行β-折叠含量>30%的PF4结构变化会使PF4/多阴离子复合物具有抗原性。此外，我们发现多磷酸盐（polyP-55）会诱导PF4发生抗原性变化，而磺达肝癸钠则不会。我们提供了一个模型，表明在涉及AA 32-38的发夹结构中会发生PF4/多阴离子复合物上暴露抗原的构象变化，这些氨基酸与相邻PF4单体的C末端AA（66-70）一起在PF4四聚体表面形成一个连续的区域，解释了为什么只有四聚体PF4分子表达“HIT抗原”。免疫测定中抗体结合与PF4结构变化的相关性提供了一种有趣的可能性，即CD光谱可能成为第一种独立于抗体的体外方法，用于预测药物的潜在免疫原性。CD光谱可以在临床前药物开发过程中识别诱导与抗原性相关的PF4结构变化的化合物。然后在临床试验中可以具体探讨其临床相关性。这些发现是否可以推广到其他内源性蛋白质还需要进一步研究。
