However, dna damage has been ruled out as the prerequisite for alkylating agents-induced mutagenesis . for example, somatic hypermutation, which occurred around the variable region in the immunoglobin gene of b cells, is driven by antigen activation not by dna damage and is considered a kind of active mutation 但是dna损伤并不是引起突变的必要条件,一个典型的例子就是发生在b淋巴细胞的免疫球蛋白(ig)可变区基因上的“体细胞超突变(somatichyermutation)”,是由表面抗原受体而不是dna损伤驱动的主动突变。