To understand the role of histone modifications in regulating MMP9 in the context of RA, the occupancy of histone acetylation marks (H3K9Ac, H4K8Ac) and histone acetyltransferase (HAT; P300, PCAF) were analyzed using the ChIP and RT-PCR methods. The gene discussed is KAT2B; the disease is rheumatoid arthritis.