Btk at the Pre-B Cell Receptor Checkpoint

textabstractSignalling from the BCR or its immature form, the pre-BCR, was shown to be crucial for B cell development. Gene-targeted mice have defined differential roles of components of the (pre-) BCR complex or its downstream signalling pathways. One of the proteins involved in (pre-) BCR signalling is the cytoplasmic protein Bruton’s tyrosine kinase (Btk). Mice deficient in Btk have B cell differentiation defects resulting in an X-linked immunodefi ciency (xid) phenotype. The xid phenotype is characterized by a reduction in the number of peripheral B cells and the residual B cell have an immature phenotype, indicating that the lack of Btk causes a block in peripheral B cell