Determination of the antibody titer To determine the titer of the antibody, an ELISA was performed using a serial dilution of the antibody against H4K5, 8, 12, 16ac in antigen coated wells. The antigen used was a peptide containing the histone modification of interest. By plotting the absorbance against the antibody dilution (Figure 3), the titer of the antibody was estimated to be 1:21, 200.