Nagaoka Y, Kabeya H, Onuma M, Kasai N, Okada K, Aida Y
Tsukuba Life Science Center, The Institute of Physical and Chemical Research (RIKEN), Ibaraki, Japan.
Cancer Res. 1999 Feb 15;59(4):975-81.
For the further characterization of bovine leukemia virus (BLV)-induced leukemogenesis, we investigated the association between polymorphism of ovine leukocyte antigen (OLA)-DRB1 gene and tumor development after infection of sheep with BLV. We infected 28 sheep with BLV and cloned exon 2 of the OLA-DRB1 gene from asymptomatic animals and from animals with lymphoma Sequence analysis revealed that, among 12 healthy sheep without any evidence of tumor, ten (83.3%) carried DRB1 alleles encoding Arg-Lys (RK) at positions beta70/71 as compared with only 6 (37.5%) of the 16 sheep with lymphoma, which suggested that alleles encoding the RK motif might protect against development of tumors after infection by BLV. By contrast, alleles encoding Ser-Arg (SR) at positions beta70/71 were present at a significantly elevated frequency in sheep with lymphoma as compared with the healthy carriers, which indicated that OLA-DRB1 alleles encoding the SR motif might be positively related to susceptibility to tumor development. The two amino acids in these motifs line a pocket that accommodates the side chain of a bound peptide according to a model of the crystal structure of human leukocyte antigen (HLA)-DR1. To analyze immunoreactions of sheep with alleles that encoded RK or SR at beta70/71, we selected sheep with either the RK/SR genotypes or the SR/SR genotypes and immunized them with a mixture of multiple synthetic antigenic peptides that corresponded to T-helper, T-cytotoxic, and B-cell epitopes of the BLV envelope glycoprotein gp51. Two weeks after the last immunization, all of the sheep were challenged with BLV. Sheep with the RK/SR genotype produced neutralizing antibodies against BLV; they eliminated BLV completely within 28 weeks of the BLV challenge, and they gave strong lymphocyte-proliferative responses to the peptides used for immunization. Moreover, such animals did not develop lymphoma. By contrast, sheep with the SR/SR genotype continued to produce BLV throughout the experimental period and developed terminal disease. Our results indicate that the differences in immunoresponse were due to differences in major histocompatibility complex class II alleles and reflected the risk of BLV-induced leukemogenesis. In addition, it appears that susceptibility to tumor development may be determined to some extent by polymorphic residues binding to antigenic peptides directly within the binding cleft of the OLA-DR molecule.
为了进一步阐明牛白血病病毒（BLV）诱导白血病发生的机制，我们研究了绵羊白细胞抗原（OLA）-DRB1基因多态性与绵羊感染BLV后肿瘤发生之间的关联。我们用BLV感染了28只绵羊，并从无症状动物和患淋巴瘤的动物中克隆了OLA-DRB1基因的第2外显子。序列分析显示，在12只无任何肿瘤迹象的健康绵羊中，有10只（83.3%）在β70/71位点携带编码精氨酸-赖氨酸（RK）的DRB1等位基因，而在16只患淋巴瘤的绵羊中只有6只（37.5%）携带该等位基因，这表明编码RK基序的等位基因可能对BLV感染后肿瘤的发生具有保护作用。相比之下，与健康携带者相比，在患淋巴瘤的绵羊中，β70/71位点编码丝氨酸-精氨酸（SR）的等位基因频率显著升高，这表明编码SR基序的OLA-DRB1等位基因可能与肿瘤发生的易感性呈正相关。根据人白细胞抗原（HLA）-DR1晶体结构模型，这些基序中的两个氨基酸形成一个口袋，用于容纳结合肽的侧链。为了分析β70/71位点编码RK或SR的绵羊的免疫反应，我们选择了具有RK/SR基因型或SR/SR基因型的绵羊，并用对应于BLV包膜糖蛋白gp51的T辅助、T细胞毒性和B细胞表位的多种合成抗原肽混合物对它们进行免疫。最后一次免疫后两周，所有绵羊均接受BLV攻击。具有RK/SR基因型的绵羊产生了针对BLV的中和抗体；它们在BLV攻击后28周内完全清除了BLV，并对用于免疫接种所用的肽产生了强烈的淋巴细胞增殖反应。此外，这些动物未发生淋巴瘤。相比之下，具有SR/SR基因型绵羊在整个实验期间持续产生BLV并发展为终末期疾病。我们的结果表明，免疫反应的差异是由于主要组织相容性复合体II类等位基因的差异所致，并且反映了BLV诱导白血病发生的风险。此外，肿瘤发生的易感性似乎在一定程度上可能由OLA-DR分子结合裂隙内直接与抗原肽结合的多态性残基决定。
