somatic recombination of immunoglobulin genes involved in immune response B cell activation involved in immune response isotype switching Note that IgM and IgD can be coexpressed by B cells via an alternate splicing mechanism, but true recombinational isotype switching to IgD has been demonstrated as well. Note that this term is best used to annotate gene products which are involved in the mechanism of DNA recombination used in isotype switching, like the B cell specific Swap70 factor in the mouse, rather than gene products which promote isotype switching such as cytokines or co-stimulatory molecules, which should instead be annotated to 'regulation of isotype switching ; GO:0045191'.