TEC also known as PSCTK4 is a member of the Tec family of non-receptor tyrosine kinases, which includes five other proteins: Emt, Btk, Bmx, Txk, and Dsrc28C. Each of these proteins contains SH3 and SH2 domains, essential for protein-protein interactions, and most also possess a pleckstrin homology (PH) domain and a Tec homology (TH) domain that facilitate membrane localization and signaling. Proper functioning of TEC is critical, as mutations can lead to immune deficiencies, such as X-linked agammaglobulinemia associated with Btk. Expression of TEC and its family members is tightly regulated, with specific isoforms being expressed in various hematopoietic lineages and tissues, underscoring their importance in both normal immune function and potential pathological conditions.