Bruton’s tyrosine kinase (BTK) is a nonreceptor tyrosine kinase and is essential in regulating signaling of multiple pathways implicated in immune-mediated disease.^1-4 

• Following antigen recognition and binding by the surface B cell receptor, BTK is recruited to the cell membrane where it becomes activated by a series of phosphorylations.²
• B cells, in addition to being a source of autoantibodies, also play a critical role in immune-mediated disease through antibody-independent mechanisms, including the action of B cells as antigen-presenting cells and as sources of pro-inflammatory cytokines.³
• BTK is also expressed to high levels in myeloid lineages and regulates the signaling pathways leading to expression of pro-inflammatory cytokines, induced through the binding of immune complexes to the Fcγ and Fcε receptors in immune-mediated disease.¹
  
• BTK mediates RANKL-dependent osteoclastogenesis from monocyte lineage precursors.⁴