BTK

Class

BTK inhibitor

Bruton's tyrosine kinase (BTK) is an intracellular signaling enzyme expressed mainly in B lymphocytes and related immune cells. It sits downstream of the B-cell receptor, a surface protein complex that recognizes antigens and triggers a cascade controlling B-cell survival, proliferation, and antibody production. In certain B-cell cancers, this signaling is chronically active, driving malignant cell growth; in autoimmune and allergic conditions, overactive B-cell and mast-cell signaling through BTK contributes to antibody-mediated tissue damage and inflammation. Inhibiting BTK interrupts this signaling relay, reducing abnormal B-cell proliferation or dampening immune activation, depending on the disease context. BTK inhibitors are small molecules that occupy the enzyme's active site; some bind irreversibly through a covalent chemical bond, while others bind reversibly, without forming a permanent attachment. Reversible binding can be useful when cancer cells develop mutations at the usual binding site that block covalent drugs, or when a shorter, more controllable duration of enzyme inhibition is desired. Because BTK also participates in normal immune defense and platelet function, its inhibition carries trade-offs between therapeutic benefit and effects on infection risk or bleeding tendency. This mechanism broadly matters across B-cell malignancies and select autoimmune and allergic diseases.