Structural analysis of protective and non-protective T-cell epitopes encoded with in the retroviral gag gene product

1)小鼠逆转录病毒gag基因产物之一n端MA蛋白含有多个t淋巴细胞表位，可被cd4阳性辅助细胞识别。其中一个辅助t细胞表位定位在氨基酸残基62和76内，另一个表位定位在MA蛋白残基119和138之间。2)对62-76表位特异性反应的cd4阳性T细胞产生大量IL-4，而对119-138表位反应的T细胞则没有。3)为了鉴定抗逆转录病毒感染所需的抗原结构，在新修饰的痘苗病毒载体中表达了各种截断形式的MA，并用重组痘苗病毒免疫小鼠。所有截断形式的MA都失去了保护小鼠的能力，而整个MA是有效的。为了阐明n端部分的截断是否由于缺乏蛋白质肉豆蔻化所需的n端残基而影响了整个MA的有效性，在突变体MA中，残基2处的Gly被Ala取代。这种突变的MA定位于细胞核，而不是豆荚状蛋白通常聚集的细胞膜，同时表达这种突变的MA的痘苗病毒失去了保护小鼠免受逆转录病毒感染的能力。4)因此，MA的肉豆蔻化是其适当的免疫原性所必需的，当肉豆蔻化时，不需要Th2表位，但需要c端部分的表位才能发挥MA的保护作用。

1) One of the mouse retroviral gag gene products, the N-terminal MA protein, contains multiple T-lymphocyte epitopes recognized by CD4-positive helper cells. One of these T-helper cell epitopes was mapped within amino acid residues 62 and 76, and another epitope was localized between residues 119 and 138 in the MA protein.2) CD4-positive T cells specifically reacting to the 62-76 epitope produced a large amount of IL-4, while T cells reactive to the epitope within 119-138 did not.3) To identify the antigenic structures that are required for protection against retroviral infection, various truncated forms of MA were expressed in a newly modified vaccinia virus vector, and mice were immunized with the resultant recombinant vaccinia viruses. All the truncated forms of MA lost the ability to protect mice, while the entire MA was effective. To elucidate if the truncation in the N-terminal portion affected the effectiveness of the whole MA due to the lack of the N-terminal residue required for protein myristylation, Gly at residue 2 was replaced with Ala in a mutant MA. This mutant MA localized in the cell nuclei, instead of cell membrane where myristylated proteins normally accumulate, and at the same time the vaccinia virus expressing this mutant MA lost its ability to protect mice against retroviral infection.4) Thus, myristylation of MA is necessary for its proper immunogenicity, and when myristylated, the Th2 epitope is not necessary, but an epitope in the C-terminal portion is required for protective efficacy of MA.