MeDIP was performed using a previously published protocol20 (link), but we also included a ligation-mediated PCR (LM-PCR) step43 (link) to amplify the material (the LM-PCR step was not performed for MeDIP-seq). Hybridizations of pre- and post-LM-PCR samples on custom tile-path arrays (2kb resolution) for the human Major Histocompatibility Complex (MHC) showed that the LM-PCR did not introduce significant bias (Supplementary Fig. 1 online). A detailed protocol is provided in the Supplementary Methods online.