Tax and MEF-2 are recruited to the HTLV-1 LTR. Chromatin immunoprecipitation of Tax protein and transcription factors bound to cellular and viral promoters during HTLV-1 infection in (A) cell lines, (B) primary CD4+ T cells, and (C) primary CD4+CD25+ T cells was performed using the ChIP-IT Express kit. Cells were lysed in a dounce homogenizer to obtain sheared chromatin following formaldehyde fixation. The sheared chromatin was immunoprecipitated at 4°C overnight using 2 μg of antibodies against the Tax protein, indicated cellular factors and controls. The immunoprecipitated chromatin was then subjected to PCR using primers for HTLV-1 LTR and human GAPDH. Data is presented as average fold change over control IgG immunoprecipitation, and is representative of three independent experiments.