Mice deficient for the type II topoisomerase-like DNA transesterase Spo11 show normal immunoglobulin somatic hypermutation and class switching

Abstract

Somatic hypermutation in B cells undergoing T cell dependent immune responses generates high affinity antibodies that provide protective immunity. B cells also switch from the expression of immunoglobulin (lg) M and lgD to that of other lg classes through somatic DNA recombination. Recent work has implicated DNA strand breaks, possibly DNA double strand breaks (DSB), as the initiating lesions in both class switch recombination and hypermutation, although the etiology of these lesions is not understood. Spo11, a protein structurally related to archaeal type II topoisomerases, generates DSB that initiate meiotic recombination. This characteristic, together with its expression pattern, marks this enzyme as a potential candidate for the initiation of hypermutation, and perhaps also for lg class switching. To investigate whether Spo11 is involved in these processes, we studied the T cell dependent immune response of Spo11-deficient (Spo11-/-) mice against the hapten nitrophenyl (NP). We found that V186.2-bearing lgG1 transcripts had normal levels and patterns of somatic hypermutation. Furthermore, Spo11-/- mice showed normal serum levels of all lg isotypes. These results indicate that Spo11 is not required for lg hypermutation or class switch recombination.