SWAP-70 is a 70 kDa multiple functional signaling proteins involved in formation of membrane ruffling induced by signal cascade of tyrosine kinase growth factor receptors. It is involved in regulating migration and invasion of trophoblast cells during the processes of embryonic implantation and placentation in primates. Though originally isolated from activated B lymphocytes, recently it has been found that it is widely expressed in various cell types and tissues. It has a high binding afinity to PI(3,4)P2. Its intracellular localization has been reported to depend on cell activation. Stimulation of the B cell receptor triggers a translocation of SWAP-70 from the cytosol to the plasma membrane in B cells. This translocation required a functional PH-domain. SWAP-70 functions as the only B cell-specific component of an isotype switch recombination complex called SWAP. The SWAP complex has specificity for the switch regions upstream of the constant region immunoglobulin genes and it facilitates the transfer of DNA between switch regions. These features suggested that mutations in the gene encoding SWAP-70 might result in humoral immunodeficiency.