Function and disease susceptibility of bovine MHC class II molecule

为探讨牛淋巴细胞抗原（BoLA）基因多态性与BLV诱发的淋巴瘤的易感性和抗性的关系，从54只BLV感染动物（无白细胞血症、持续性淋巴细胞增多和淋巴瘤3个独立阶段）中克隆了BoLA-DRB 3基因的第2外显子，并测定了其核苷酸序列。序列分析表明，BoLA-DRB 3等位基因编码的瓦尔在第78位可能与BLV诱导的淋巴瘤的抗性。编码第78位瓦尔的等位基因的特征在于Arg或Lys，其代表第71位的正电荷，以及Glu，其代表第74位的负电荷。与此相反，编码78位Tyr的等位基因具有代表74位中性电荷的氨基酸如Ala、Asn或Tyr，并且与淋巴瘤易感性相关。38%携带绵羊白细胞抗原（奥拉）-DRB 1 Arg^<70>-Lys^<71>（RK）的特异性等位基因，而在12只无症状期BLV感染绵羊中为83%。为了分析OLA-DRB 1 RK等位基因绵羊的免疫反应，我们用BLV囊膜糖蛋白gp 51的辅助性T细胞、细胞毒T细胞和B细胞表位的复合抗原肽免疫RK/X基因型和X/X基因型绵羊，最后一次免疫后2周，所有绵羊用BLV感染绵羊的血液进行攻击。携带抗性等位基因的绵羊对混合肽表现出高的免疫应答，且未发生白血病。我们的研究结果表明，免疫反应的差异导致由于MHC II类等位基因的差异，并涉及BLV诱导白血病的风险。

To investigate the relationship between polymorphism of bovine lymphocyte antigen (BoLA) gene and resistance or susceptibility to BLV-induced lymphoma, exon 2 of the BoLA-DRB3 gene which is highly polymorphic was cloned from 54 BLV-infected animals with 3 independent stages such as an aleukemic healthy, persistent lymphocytosis and lymphoma, and the nucleotide sequences were determined. Sequence analysis revealed that the BoLA-DRB3 alleles encoding Val at position 78 may be associated with resistance to BLV-induced lymphoma. Alleles encoding Val at position 78 were characterized by Arg or Lys, which represent a positive charge at position 71 and by Glu, which represents a negative charge at position 74. By contrast, alleles encoding Tyr at position 78, have amino acids such as Ala, Asn or Tyr, which represent a neutral charge at position 74 and were associated with susceptibility to lymphoma.Next, to confirm the association between polymorphism of MHC class II gene and leukemia, we infected 28 sheep with BLV.Among the 16 sheep with lymphoma, 38% carry specific alleles of the ovine leukocyte antigen (OLA)-DRB1 Arg^<70>-Lys^<71> (RK) as compared to 83% among the 12 BLV-infected sheep at the asymptomatic stage. To analyze the immunoreaction of sheep with allele of OLA-DRB1 RK, we immunized sheep carrying either a RK/X genotype or a X/X genotype with a mixture of synthetic multiple antigenic peptides of T-helper, T-cytotoxic, and B-cell epitopes of BLV envelope glycoprotein gp 51, and two weeks after the last immunization, all sheep were challenged with blood from a BLV-infected sheep. Sheep carrying resistant allele showed high immunoresponse against the mixed peptides and did not proceeded to ieukemia. Our results indicate that difference of immunoresponse resulted due to difference of MHC class II alleles and involved the risk of BLV-induced leukemogenesis.