Perlmutter A P, Gilbert W
Proc Natl Acad Sci U S A. 1984 Nov;81(22):7189-93. doi: 10.1073/pnas.81.22.7189.
A few percent of mouse splenocytes express isotypes characteristic of the secondary response together with IgM, and some cells express these isotypes alone. We isolated populations of small memory cells that express (i) IgM but not IgG1, (ii) IgM but not IgA, (iii) IgM and IgG1, (iv) IgM and IgA, and (v) IgG1 but not IgM. We have analyzed their DNA to show that there has been no switch recombination or deletion in the Ig constant region (C) genes. Using sandwich RNA hybridizations, we have found that cells expressing IgG1 contain nuclear RNAs that have both C mu and C gamma 1 sequences, and that cells expressing IgA contain nuclear RNAs that have both C mu and C alpha sequences. We propose that the expression of an isotype characteristic of the secondary response in memory cells is accomplished by alternative RNA processing of large (up to 180 kilobases) nuclear RNA transcripts that span the heavy chain gene locus.
百分之几的小鼠脾细胞表达与IgM一起的二次应答特征性同种型，并且一些细胞单独表达这些同种型。我们分离出了表达以下情况的小记忆细胞群体：(i) IgM但不表达IgG1，(ii) IgM但不表达IgA，(iii) IgM和IgG1，(iv) IgM和IgA，以及(v) IgG1但不表达IgM。我们分析了它们的DNA，以表明在Ig恒定区(C)基因中没有发生转换重排或缺失。使用夹心RNA杂交，我们发现表达IgG1的细胞含有同时具有Cμ和Cγ1序列的核RNA，并且表达IgA的细胞含有同时具有Cμ和Cα序列的核RNA。我们提出，记忆细胞中二次应答特征性同种型的表达是通过跨越重链基因座的大（高达180千碱基）核RNA转录本的选择性RNA加工来实现的。
