Hurwitz J L, Coleclough C, Cebra J J
Cell. 1980 Nov;22(2 Pt 2):349-59. doi: 10.1016/0092-8674(80)90345-1.
To probe mechanisms operating at the CH gene locus during normal B lymphocyte differentiation, we have used cloned probes for the constant region genes Cmu, C gamma 1 and C alpha to analyze the immunoglobulin heavy chain genes of three kinds of cell populations in successive stages of B cell development. These are IGM-bearing B lymphocytes from the normal spleen of unprimed mice, hybridomas prepared by fusing spleen cells from antigen-primed mice with the SP2/O permanent cell line and selected to secrete one of five different isotypes (IgM, IgG3, IgG1, IgG2 and IgA) and a set of plasmacytoma lines. The IgM-bearing B cells carry Cmu genes with rearrangements between VH and JH genes on both chromosomes even though only one chromosome is expressed; clearly, allelic exclusion cannot be explained by the lack of CH gene rearrangement on the nonexpressed chromosome. The normal splenic DNA component of antibody-secreting hybridomas displays rearrangements between JH and Cmu genes as well as among CH genes other than Cmu, with concomitant deletion of CH genes 5' to those expressed. These CH rearrangements and deletions are likely to accompany the isotype switching process and may occur on both expressed and nonexpressed chromosomes. We used hybridomas (spleen-derived), which secrete primarily IgM, and plasmacytomas (gut-derived), which secrete primarily IgA, to represent plasma cells in early and late stages of differentiation, respectively. A direct comparison of hybridomas and plasmacytomas making the same products (IgG3 or IgG1) indicates that hybridomas display a low frequency (2/12) of nonexpressed C alpha gene rearrangements in contrast to the high frequency (7/10) displayed by plasma-cytomas. We propose that CH gene switching rearrangements and deletions may occur successively along the CH gene locus, involving any of the undeleted genes at each step. These can occur on both expressed and nonexpressed chromosomes during the normal clonal outgrowth of a B cell line in vivo, and would result in the accumulation of both productive and nonproductive rearrangements of the presumed last CH gene, C alpha.
为了探究正常B淋巴细胞分化过程中CH基因座的作用机制，我们使用了针对恒定区基因Cmu、Cγ1和Cα的克隆探针，来分析B细胞发育连续阶段中三种细胞群体的免疫球蛋白重链基因。这些细胞群体分别是来自未免疫小鼠正常脾脏的携带IgM的B淋巴细胞、通过将抗原免疫小鼠的脾脏细胞与SP2/O永久细胞系融合制备并经筛选可分泌五种不同同种型（IgM、IgG3、IgG1、IgG2和IgA）之一的杂交瘤，以及一组浆细胞瘤系。携带IgM的B细胞携带Cmu基因，其两条染色体上的VH和JH基因之间均发生了重排，尽管仅一条染色体表达；显然，等位基因排斥不能用未表达染色体上缺乏CH基因重排来解释。分泌抗体的杂交瘤的正常脾脏DNA成分在JH和Cmu基因之间以及除Cmu之外的其他CH基因之间显示出重排，同时伴随着5'端至所表达CH基因的CH基因缺失。这些CH重排和缺失可能伴随着同种型转换过程，并且可能在表达和未表达的染色体上均发生。我们使用主要分泌IgM的（源自脾脏的）杂交瘤和主要分泌IgA的（源自肠道的）浆细胞瘤，分别代表分化早期和晚期的浆细胞。对产生相同产物（IgG3或IgG1）的杂交瘤和浆细胞瘤进行直接比较表明，杂交瘤中未表达的Cα基因重排频率较低（2/12），而浆细胞瘤显示出较高的频率（7/10）。我们提出，CH基因转换重排和缺失可能沿着CH基因座依次发生，每一步涉及任何未缺失的基因。这些重排和缺失可在体内B细胞系正常克隆扩增过程中在表达和未表达的染色体上发生，并将导致假定的最后一个CH基因Cα的有 productive 和无 productive 重排的积累。
