BCL-6 protein is a transcriptional repressor that plays a crucial role in the regulation of B cell differentiation and proliferation. It is primarily expressed in germinal center B cells and is essential for the formation and function of germinal centers, which are specialized microenvironments within lymphoid tissues where B cells undergo somatic hypermutation and class switch recombination to generate high-affinity antibodies. BCL-6 achieves its regulatory functions by binding to specific DNA sequences in the promoters of target genes, thereby inhibiting their transcription. Abnormal expression or function of BCL-6 is associated with various B cell lymphomas, making it an important biomarker and therapeutic target in the study and treatment of these malignancies.