Sorted splenic B cells were fixed with 1% formaldehyde at room temperature for 10 mins followed by quenching with 0.125M glycine (final concentration). The cells were washed twice with ice cold PBS containing protease inhibitors (1mM phenylmethylsulfonyl fluoride (PMSF), 1 ug/ml aprotinin and 1ug/ml pepstatin A), harvested and treated with SDS lysis buffer for 10 min on ice. Resulting lysates were sonicated to shear the DNA to fragment lengths of 200 to 500bp. 10 ng chromatin immunoprecipitated DNA was used for each library prep using Illumina Truseq Chip Library Prep Kit according to the manufacturer’s instructions