B-cell lymphoma 6 (Bcl-6), is an 80 kD homodimer and member of the BTB-POZ zinc finger family. It consists of one BTB (POZ) domain and six C2H2-type zinc fingers. Bcl-6 is a transcriptional repressor as well as a master regulator of germinal center reaction. On B cells, Bcl-6 induces proliferation, antibody class switching and affinity maturation, while inhibits its differentiation to plasma cells. On T cells, Bcl-6 induces its differentiation to TFH. This molecule is also expressed in some B cell lymphomas and breast cancer cells.