Antigenic Variation of East/Central/South African and Asian Chikungunya Virus Genotypes in Neutralization by Immune Sera

BackgroundChikungunya virus (CHIKV) is a re-emerging mosquito-borne virus which causes epidemics of fever, severe joint pain and rash. Between 2005 and 2010, the East/Central/South African (ECSA) genotype was responsible for global explosive outbreaks across India, the Indian Ocean and Southeast Asia. From late 2013, Asian genotype CHIKV has caused outbreaks in the Americas. The characteristics of cross-antibody efficacy and epitopes are poorly understood.Methodology/Principal FindingsWe characterized human immune sera collected during two independent outbreaks in Malaysia of the Asian genotype in 2006 and the ECSA genotype in 2008–2010. Neutralizing capacity was analyzed against representative clinical isolates as well as viruses rescued from infectious clones of ECSA and Asian CHIKV. Using whole virus antigen and recombinant E1 and E2 envelope glycoproteins, we further investigated antibody binding sites, epitopes, and antibody titers. Both ECSA and Asian sera demonstrated stronger neutralizing capacity against the ECSA genotype, which corresponded to strong epitope-antibody interaction. ECSA serum targeted conformational epitope sites in the E1-E2 glycoprotein, and E1-E211K, E2-I2T, E2-H5N, E2-G118S and E2-S194G are key amino acids that enhance cross-neutralizing efficacy. As for Asian serum, the antibodies targeting E2 glycoprotein correlated with neutralizing efficacy, and I2T, H5N, G118S and S194G altered and improved the neutralization profile. Rabbit polyclonal antibody against the N-terminal linear neutralizing epitope from the ECSA sequence has reduced binding capacity and neutralization efficacy against Asian CHIKV. These findings imply that the choice of vaccine strain may impact cross-protection against different genotypes.Conclusion/SignificanceImmune serum from humans infected with CHIKV of either ECSA or Asian genotypes showed differences in binding and neutralization characteristics. These findings have implications for the continued outbreaks of co-circulating CHIKV genotypes and effective design of vaccines and diagnostic serological assays.

背景：基孔肯雅病毒（Chikungunya virus, CHIKV）是一种再现的虫媒传播病毒，可引发发热、剧烈关节痛及皮疹相关的疫情。2005年至2010年间，东/中非/南非（East/Central/South African, ECSA）基因型病毒在印度、印度洋区域及东南亚地区引发了全球性暴发疫情。2013年末起，亚洲基因型基孔肯雅病毒在美洲地区引发多起暴发事件。目前学界对其交叉抗体效力及表位的特征尚缺乏深入认知。
研究方法与主要结果：本研究对马来西亚两次独立暴发疫情中采集的人类免疫血清进行了表征，分别为2006年亚洲基因型疫情与2008-2010年ECSA基因型疫情。我们针对代表性临床分离株，以及从ECSA与亚洲基因型基孔肯雅病毒感染性克隆中拯救得到的病毒，分析了血清的中和活性。本研究进一步采用全病毒抗原与重组E1、E2包膜糖蛋白，探究了抗体结合位点、表位及抗体滴度。
结果显示，ECSA型与亚洲型免疫血清均对ECSA基因型病毒表现出更强的中和活性，这与较强的表位-抗体相互作用相契合。ECSA型免疫血清靶向E1-E2糖蛋白的构象表位位点，其中E1-E211K、E2-I2T、E2-H5N、E2-G118S及E2-S194G为增强交叉中和效力的关键氨基酸残基。针对亚洲型免疫血清，靶向E2糖蛋白的抗体水平与中和活性呈显著相关，而I2T、H5N、G118S及S194G位点可改变并优化病毒的中和谱。针对ECSA序列N端线性中和表位制备的兔多克隆抗体，对亚洲基因型基孔肯雅病毒的结合能力与中和活性均有所下降。上述结果提示，疫苗株的选择可能会影响针对不同基因型病毒的交叉保护效果。
结论与意义：感染ECSA或亚洲基因型基孔肯雅病毒的人类免疫血清，其抗体结合与中和特征存在显著差异。该研究结果对于当前共循环的基孔肯雅病毒基因型持续暴发疫情，以及疫苗与诊断血清学检测方法的优化设计具有重要参考价值。