ZBTB7B belongs to a large family of transcription factors, generally acting as repressors, characterized by a carboxy-terminal DNA binding domain made of multiple zinc fingers (four in Thpok) and an amino-terminal BTB-POZ domain that mediates homo- (and possibly hetero-) dimerization [PMID: 17084908]. Zbtb7b is up-regulated by MHC-II-restricted thymocytes during their CD4 differentiation and is a major determinant of CD4 lineage choice. Two properties of ZBTB7B deserve attention. First, although Thpok is expressed in a wide variety of cells, its expression in the thymus is highly lineage-specific : CD4 SP thymocytes (and all CD4 T cells) express Thpok, whereas DP and CD8 SP thymocytes do notSecond, both loss- and gain-of-function experiments indicate that Thpok affects lineage choice but not positive selection [PMID: 15729333, 10550051].