腸病毒71型（EV71）是造成手足口病（HFMD）的主要病原體之一，兒童感染後可能會引發嚴重的神經併發症而導致死亡，由於目前尚無專門對抗EV71的藥物或治療方式，因此發展疫苗被認為是控制腸病毒疫情的重要手段。本研究將EV71的VP1基因分別與FAI3及Mig(IgG)兩種IgG結合蛋白的基因進行融合，並藉大腸桿菌表現生產rVP1、rVP1-FAI3及rVP1-Mig(IgG)三種重組蛋白質，以對小鼠進行口服疫苗測試。結果顯示，這三種重組蛋白質的餵食處理皆能使小鼠糞便內及血液中的VP1抗體效價提升，並呈現典型的一級和二級免疫反應情形，證實這些重組蛋白質的餵食處理不僅能激活小鼠的黏膜性及系統性免疫反應，並能促使小鼠體內產生針對VP1抗原的記憶性B細胞。三種重組蛋白質的餵食處理中，融合蛋白[rVP1-Mig(IgG)及rVP1-FAI3]餵食組的VP1抗體效價明顯高於rVP1餵食組：在血液中，前者為後者的1.47~2.02倍；在糞便內，前者則為後者的2.04~2.62倍。這些結果顯示FAI3及Mig(IgG)具有黏膜性佐劑的性質，共同表現這兩種IgG結合蛋白將可增進rVP1作為腸病毒口服疫苗的功效。本研究經由ELISA及細胞染色的實驗，已證實rVP1-FAI3及rVP1-Mig(IgG)能與小鼠的IgG及脾臟細胞表面結合，而小鼠與人類IgG CH2－CH3 domain的胺基酸序列有高達70%的相同度，因此我們推論FAI3及Mig(IgG)兩種IgG結合蛋白具有應用於開發人類口服疫苗的潛力。

Enterovirus 71 (EV71) is the main infective agent of hand, foot and mouth disease (HFMD) and may cause fatal neurological complications and death among young children. Due to the lack of an effective antiviral agent, developing useful vaccines is considered a top choice among all control measures. In this study, the genes encoding two IgG binding proteins, FAI3 and Mig(IgG), were fused to VP1 gene respectively, and three recombinant proteins, rVP1, rVP1-FAI3 and rVP1-Mig(IgG), was individually expressed in E. coli and used for oral immunization tests in mice. Our results revealed that feeding each of these three recombinant proteins to mice can elevate the titers of VP1 antibodies in both serum and feces, and the changing of antibody titer displays a typical pattern of primary and secondary immune responses, suggesting our feeding strategy is effective in activating both mucosal and systemic immune responses and in causing generation of specific memory B cells. Among the three recombinant proteins, fusion proteins [rVP1-Mig(IgG) and rVP1-FAI3] were found to stimulate significantly higher VP1 antibody titer, both in serum and feces, than that by rVP1. These data manifest the mucosal adjuvant property of FAI3 and Mig(IgG) and thus co-expression of these two IgG-binding proteins should be able to enhance the efficacy of rVP1 as oral vaccine for EV71. Moreover, since our results of ELISA and cell surface staining demonstrate the binding ability of rVP1-FAI3 and rVP1-Mig(IgG) to mouse IgGs and spleen cells, and since the amino acid sequence of mouse IgG CH2－CH3 domain is 70% identical to that of human’s counterpart, it is inferred that FAI3 and Mig(IgG) may also be used as mucosal adjuvant for human.

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