New roots for IgE-producing B cells.

In allergic responses, B cells are driven to undergo an immunoglobulin isotype switch, shifting from immunoglobulin M to immunoglobulin E (IgE) synthesis. This process involves the rearrangement of germline DNA in the immunoglobulin heavy-chain locus and is stimulated by cytokines (IL-4 and IL-13) and CD40 activation, but the biology of the IgE-producing B cells, where they are located when the isotype switch occurs as well if the process involves an intermediate step of rearrangement to IgG1 and later to IgE, is still poorly understood.