Levy N S, Malipiero U V, Lebecque S G, Gearhart P J
Department of Biochemistry, Johns Hopkins University School of Hygiene and Public Health, Baltimore, Maryland 21205.
J Exp Med. 1989 Jun 1;169(6):2007-19. doi: 10.1084/jem.169.6.2007.
The dynamics of somatic mutation in Ig variable genes was investigated in order to define a population of B cells undergoing mutation. BALB/cJ mice were injected with PC-KLH, and splenic RNA was prepared 5, 7, and 13 d later. The mRNA was annealed to gamma constant region primers to make cDNA transcripts encoding VH genes. 103 cDNA clones corresponding to 18 different genes from the VH7183, VH3660, and VHS107 subfamilies were sequenced to identify mutation. VH genes had a low level of mutation on day 5 after immunization and accumulated more mutation by day 7 at a rate of 10(-3) mutations per nucleotide per generation. However, by day 13, the number of mutations per gene did not increase, and most of the substitutions encoded replacement amino acid changes that were clustered in the hypervariable regions, indicating that the mutational process was less active during the second week and that antigen selection had occurred. The data are consistent with a developmentally regulated mechanism in which mutation is activated during the first week of the primary immune response for a limited time period, after which selection acts to preserve the beneficial mutants.
为了确定正在发生突变的B细胞群体，研究了Ig可变基因中体细胞突变的动态变化。给BALB/cJ小鼠注射PC-KLH，并在5、7和13天后制备脾RNA。将mRNA与γ恒定区引物退火以制备编码VH基因的cDNA转录本。对来自VH7183、VH3660和VHS107亚家族的18个不同基因的103个cDNA克隆进行测序以鉴定突变。VH基因在免疫后第5天的突变水平较低，到第7天以每代每核苷酸10(-3)个突变的速率积累了更多突变。然而，到第13天，每个基因的突变数量没有增加，并且大多数取代编码了聚集在高变区的替换氨基酸变化，这表明在第二周突变过程不太活跃，并且已经发生了抗原选择。这些数据与一种发育调控机制一致，即在初次免疫反应的第一周内，突变在有限的时间段内被激活，之后选择作用于保留有益的突变体。
