Mertens P P, Burroughs J N, Walton A, Wellby M P, Fu H, O'Hara R S, Brookes S M, Mellor P S
Institute for Animal Health, Pirbright Laboratory, Woking, Surrey, United Kingdom.
Virology. 1996 Mar 15;217(2):582-93. doi: 10.1006/viro.1996.0153.
Previous studies (Mertens et al., Virology 157, 375-386, 1987) have shown that removal of the outer capsid layer from bluetongue virus (BTV) significantly reduces (approximately x 10(-4)) the infectivity of the resultant core particle for mammalian cells (BHK 21 cells). In contrast, the studies reported here, using a cell line (KC cells) derived from a species of Culicoides that can act as a vector for BTV (Culicoides variipennis), demonstrated a much higher infectivity of core particles than that in mammalian cells (approximately x 10(3)). This increase resulted in a specific infectivity for cores that was only 20-fold less than that of purified disaggregated virus particles (stored in the presence of 0.1% sodium-N-lauroylsarcosine (NLS)). Removal of this detergent caused intact virus particle aggregation and (as previously reported) resulted in an approximately 1 log10 drop in the specific infectivity of those virus particles which remained in suspension. In consequence the specific infectivity of core particles for the KC cells was directly comparable to that of the intact but aggregated virus. These data are compared with the results from oral infectivity studies using two vector species (C. variipennis and Culicoides nubeculosus), which showed similar infection rates at comparable concentrations of purified cores, or of the intact but aggregated virus particles (NLS was toxic to adult flies). The role of the outer core proteins (VP7) in cell attachment and penetration, as an alternative route of initiation of infection, is discussed. Previous studies (Mertens et al., Virology 157, 375-386, 1987) also showed that the outer capsid layer of BTV can be modified by proteases (including trypsin or chymotrypsin), thereby generating infectious subviral particles (ISVP). The specific infectivity of ISVP for mammalian cells (BHK21 cells) was shown to be similar to that of disaggregated virus particles. In contrast, we report a significantly higher specific infectivity of ISVP but not of the intact virus (approximately x 100) for two insect cell lines (KC cells and C6/36 mosquito cells (derived from Aedes albopictus)). In oral infection studies with adults of the two vector species, ISVP produced the same infection rate at approximately 100-fold lower concentrations than either core particles or the intact but aggregated virus particles. The importance of mammalian host serum proteases, or insect gut proteases, in modification of the intact virus particle to form ISVP and their role in initiation of infection and the vector status of the insect is discussed.
先前的研究（Mertens等人，《病毒学》157卷，375 - 386页，1987年）表明，去除蓝舌病毒（BTV）的外衣壳层会显著降低（约为10的 - 4次方倍）所得核心颗粒对哺乳动物细胞（BHK 21细胞）的感染性。相比之下，本研究使用源自一种可作为BTV传播媒介的库蠓物种（Culicoides variipennis）的细胞系（KC细胞），结果显示核心颗粒在其中的感染性比在哺乳动物细胞中高得多（约为10的3次方倍）。这种增加使得核心颗粒的比感染性仅比纯化的解聚病毒颗粒（在0.1% N - 月桂酰肌氨酸钠（NLS）存在下储存）低20倍。去除这种去污剂会导致完整病毒颗粒聚集，并且（如先前报道）会使仍悬浮的那些病毒颗粒的比感染性下降约1个对数单位。因此，核心颗粒对KC细胞的比感染性与完整但聚集的病毒的比感染性直接相当。这些数据与使用两种传播媒介物种（C. variipennis和Culicoides nubeculosus）进行的口服感染研究结果进行了比较，结果表明在相当浓度的纯化核心颗粒或完整但聚集的病毒颗粒情况下，感染率相似（NLS对成年果蝇有毒）。本文讨论了外核心蛋白（VP7）在细胞附着和穿透方面作为感染起始的替代途径的作用。先前的研究（Mertens等人，《病毒学》157卷，375 - 386页，1987年）还表明，BTV的外衣壳层可被蛋白酶（包括胰蛋白酶或胰凝乳蛋白酶）修饰，从而产生感染性子病毒颗粒（ISVP）。ISVP对哺乳动物细胞（BHK21细胞）的比感染性与解聚病毒颗粒的相似。相比之下，我们报告了ISVP对两种昆虫细胞系（KC细胞和C6/36蚊细胞（源自白纹伊蚊））具有显著更高的比感染性，但完整病毒则不然（约为100倍）。在对两种传播媒介物种的成虫进行的口服感染研究中，ISVP在浓度比核心颗粒或完整但聚集的病毒颗粒低约100倍的情况下产生相同的感染率。本文讨论了哺乳动物宿主血清蛋白酶或昆虫肠道蛋白酶在将完整病毒颗粒修饰形成ISVP中的重要性，以及它们在感染起始和昆虫传播媒介状态中的作用。
