Bruton's tyrosine kinase (BTK)

Class

BTK inhibitor (oral)

Pathway

B-cell receptor / myeloid cell signaling

Bruton's tyrosine kinase (BTK) is an intracellular enzyme that relays signals from the B-cell receptor, a surface protein complex through which B lymphocytes sense antigens. When the receptor is engaged, BTK is activated and propagates a signaling cascade that drives B-cell survival, proliferation, and antibody production. BTK is also expressed in myeloid cells, including microglia and macrophages, where it contributes to innate immune activation such as Fc receptor and Toll-like receptor signaling. Because dysregulated B-cell and myeloid signaling contributes to autoimmune and inflammatory conditions, and to certain B-cell malignancies, BTK has become a target for small-molecule inhibitors taken orally. By blocking BTK's catalytic activity, these agents dampen downstream signaling, reducing pathological B-cell expansion or antibody-driven inflammation, and can also modulate innate immune contributions to tissue damage. This dual relevance to adaptive and innate immunity has made BTK inhibition of interest not only in hematologic cancers but also in autoimmune and neuroinflammatory diseases, including conditions where microglial activation within the central nervous system is thought to sustain chronic inflammation. The clinical rationale depends on which cell populations and tissues a given inhibitor can effectively reach and inhibit.