Sehgal D, Mage R G, Schiaffella E
Molecular Immunogenetics Section, Laboratory of Immunology, National Institute of Allergy and Infectious Diseases, Bethesda, MD 20892, USA.
J Immunol. 1998 Feb 1;160(3):1246-55.
We investigated the molecular basis for the appearance of V(H)a2 allotype-bearing B cells in mutant Alicia rabbits. The mutation arose in an a2 rabbit; mutants exhibit altered expression of V(H) genes because of a small deletion encompassing V(H)1a2, the 3'-most gene in the V(H) locus. The V(H)1 gene is the major source of V(H)a allotype because this gene is preferentially rearranged in normal rabbits. In young homozygous ali/ali animals, the levels of a2 molecules found in the serum increase with age. In adult ali/ali rabbits, 20 to 50% of serum Igs and B cells bear a2 allotypic determinants. Previous studies suggested that positive selection results in expansion of a2 allotype-bearing B cells in the appendix of young mutant ali/ali rabbits. We separated appendix cells from a 6-wk-old Alicia rabbit by FACS based on the expression of surface IgM and a2 allotype. The VDJ portion of the expressed Ig mRNA was amplified from the IgM+ a2+ and IgM+ a2- populations by reverse transcriptase-PCR. The cDNAs from both populations were cloned and sequenced. Analysis of these sequences suggested that, in a2+ B cells, the first D proximal functional gene in Alicia rabbits, V(H)4a2, rearranged and was altered further by a gene conversion-like mechanism. Upstream V(H) genes were identified as potential gene sequence donors; V(H)9 was found to be the most frequently used gene donor. Among the a2- B cells, y33 was the most frequently rearranged gene.
我们研究了突变的艾丽西亚兔中携带V(H)a2同种异型的B细胞出现的分子基础。该突变发生在一只a2兔中；由于一个小的缺失，包括V(H)1a2（V(H)基因座中最靠近3'端的基因），突变体表现出V(H)基因表达的改变。V(H)1基因是V(H)a同种异型的主要来源，因为该基因在正常兔中优先重排。在年轻的纯合ali/ali动物中，血清中发现的a2分子水平随年龄增加。在成年ali/ali兔中，20%至50%的血清免疫球蛋白和B细胞带有a2同种异型决定簇。先前的研究表明，阳性选择导致年轻突变ali/ali兔阑尾中携带a2同种异型的B细胞扩增。我们根据表面IgM和a2同种异型的表达通过荧光激活细胞分选术（FACS）从一只6周龄的艾丽西亚兔中分离出阑尾细胞。通过逆转录聚合酶链反应（RT-PCR）从IgM+ a2+和IgM+ a2-群体中扩增出表达的Ig mRNA的VDJ部分。对这两个群体的cDNA进行克隆和测序。对这些序列的分析表明,在a2+ B细胞中，艾丽西亚兔中第一个靠近D的功能性基因V(H)4a2发生重排，并通过一种类似基因转换的机制进一步改变。上游V(H)基因被确定为潜在的基因序列供体；发现V(H)9是最常用的基因供体。在a2- B细胞中，y33是最常重排的基因。
