Grégoire Sylvie, Bergot Anne Sophie, Féraudet Cécile, Carnaud Claude, Aucouturier Pierre, Rosset Martine Bruley
Institut National de la Santé et de la Recherche Médicale Unité 712 and Université Pierre et Marie Curie, Hôpital Saint-Antoine, Paris, France.
J Immunol. 2005 Nov 15;175(10):6443-9. doi: 10.4049/jimmunol.175.10.6443.
Abs to the prion protein (PrP) can protect against experimental prion infections, but efficient Ab responses are difficult to generate because PrP is expressed on many tissues and induces a strong tolerance. We previously showed that immunization of wild-type mice with PrP peptides and CpG oligodeoxynucleic acid overcomes tolerance and induces cellular and humoral responses to PrP. In this study, we compared Ab and T cell repertoires directed to PrP in wild-type and PrP knockout (Prnp o/o) C57BL/6 mice. Animals were immunized with mouse PrP-plasmid DNA or with 30-mer overlapping peptides either emulsified in CFA or CpG/IFA. In Prnp o/o mice, Abs raised by PrP-plasmid DNA immunization recognized only N-terminal PrP peptides; analyses of Ab responses after PrP peptide/CFA immunization allowed us to identify six distinct epitopes, five of which were also recognized by Abs raised by PrP peptides/CpG. By contrast, in wild-type mice, no Ab response was detected after PrP-plasmid DNA or peptide/CFA immunization. However, when using CpG, four C-terminal peptides induced Abs specific for distinct epitopes. Importantly, immune sera from Prnp o/o but not from wild-type mice bound cell surface PrP. Abs of IgG1 and IgG2b subclasses predominated in Prnp o/o mice while the strongest signals were for IgG2b in wild-type mice. Most anti-PrP Th cells were directed to a single epitope in both Prnp o/o and wild-type mice. We conclude that endogenous PrPC expression profoundly affects the Ab repertoire as B cells reactive for epitopes exposed on native PrPC are strongly tolerized. Implications for immunotherapy against prion diseases are discussed.
针对朊病毒蛋白（PrP）的抗体可抵御实验性朊病毒感染，但由于PrP在许多组织中表达并诱导强烈的耐受性，因此难以产生有效的抗体反应。我们之前表明，用PrP肽和CpG寡脱氧核酸免疫野生型小鼠可克服耐受性，并诱导针对PrP的细胞和体液反应。在本研究中，我们比较了野生型和PrP基因敲除（Prnp o/o）C57BL/6小鼠中针对PrP的抗体和T细胞库。用小鼠PrP质粒DNA或用在CFA或CpG/IFA中乳化的30聚体重叠肽免疫动物。在Prnp o/o小鼠中，PrP质粒DNA免疫产生的抗体仅识别N端PrP肽；对PrP肽/CFA免疫后的抗体反应分析使我们能够鉴定出六个不同的表位，其中五个也被PrP肽/CpG产生的抗体识别。相比之下，在野生型小鼠中，PrP质粒DNA或肽/CFA免疫后未检测到抗体反应。然而，当使用CpG时，四种C端肽诱导出针对不同表位的特异性抗体。重要的是，来自Prnp o/o小鼠而非野生型小鼠的免疫血清结合细胞表面PrP。在Prnp o/o小鼠中，IgG1和IgG2b亚类的抗体占主导，而在野生型小鼠中最强的信号是针对IgG2b。在Prnp o/o和野生型小鼠中，大多数抗PrP Th细胞都针对单个表位。我们得出结论，内源性PrPC表达深刻影响抗体库，因为对天然PrPC上暴露的表位有反应的B细胞受到强烈耐受。讨论了对朊病毒疾病免疫治疗的意义。
