Fu T M, Mylin L M, Schell T D, Bacik I, Russ G, Yewdell J W, Bennink J R, Tevethia S S
Department of Microbiology and Immunology, Pennsylvania State University College of Medicine, Hershey 17033, USA.
J Virol. 1998 Feb;72(2):1469-81. doi: 10.1128/JVI.72.2.1469-1481.1998.
An immunological hierarchy among three H-2Db-restricted cytotoxic T lymphocyte (CTL) determinants in simian virus 40 (SV40) large T antigen (Tag) was described previously: determinants I and II/III are immunodominant, whereas determinant V is immunorecessive. To assess the immunogenicity of each determinant individually and define mechanisms that contribute to the immunorecessive nature of determinant V, we constructed a panel of recombinant vaccinia viruses (rVVs) expressing minigenes encoding these determinants in various polypeptide contexts. We found the following. (i) Immunization of mice with an rVV encoding full-length SV40 Tag resulted in priming for CTL responses to determinants I and II/III but not determinant V. (ii) rVVs encoding peptide I or II/III in the cytosol or targeted to the endoplasmic reticulum (ER) were highly antigenic and immunogenic. (iii) rVVs encoding peptide V minigenes were antigenic and immunogenic if the peptide was targeted to the ER, expressed in the cytosol with short flanking sequences, or expressed from within a self-protein, murine dihydrofolate reductase. (iv) Presentation of the nonflanked peptide V (preceded by a Met codon only) could be enhanced by using a potent inhibitor of the proteasome. (v) H-2Db-epitope V peptide complexes decayed more rapidly than complexes containing epitope I or II/III peptides. In brefeldin A blocking experiments, functional epitope V complexes were detected longer on targets expressing ER-targeted epitope V than on targets expressing forms of epitope V dependent on the transporter associated with antigen processing. Therefore, limited formation of relatively unstable cell surface H-2Db complexes most likely contributes to the immunorecessive nature of epitope V within SV40 Tag. Increasing the delivery of epitope V peptide to the major histocompatibility complex class I presentation pathway by ER targeting dramatically enhanced the immunogenicity of epitope V.
先前已描述了猿猴病毒40（SV40）大T抗原（Tag）中三个H-2Db限制性细胞毒性T淋巴细胞（CTL）决定簇之间的免疫层级关系：决定簇I和II/III具有免疫显性，而决定簇V具有免疫隐性。为了单独评估每个决定簇的免疫原性，并确定导致决定簇V免疫隐性的机制，我们构建了一组重组痘苗病毒（rVVs），它们在各种多肽背景下表达编码这些决定簇的小基因。我们发现如下情况。（i）用编码全长SV40 Tag的rVV免疫小鼠可引发针对决定簇I和II/III而非决定簇V的CTL反应。（ii）在细胞质中或靶向内质网（ER）的编码肽I或II/III的rVVs具有高度抗原性和免疫原性。（iii）如果肽靶向ER、在细胞质中与短侧翼序列一起表达或从自身蛋白小鼠二氢叶酸还原酶内部表达，则编码肽V小基因的rVVs具有抗原性和免疫原性。（iv）使用蛋白酶体的强效抑制剂可增强无侧翼肽V（仅在前面有一个Met密码子）的呈递。（v）H-2Db-表位V肽复合物比含有表位I或II/III肽的复合物更快衰变。在布雷菲德菌素A阻断实验中，在表达ER靶向表位V的靶细胞上检测到功能性表位V复合物的时间比在表达依赖于与抗原加工相关转运体的表位V形式的靶细胞上更长。因此，相对不稳定的细胞表面H-2Db复合物形成受限很可能导致了SV40 Tag内表位V的免疫隐性。通过ER靶向增加表位V肽向主要组织相容性复合体I类呈递途径的递送显著增强了表位V的免疫原性。
