Anti-P55 antibodies enable researchers to detect and measure the P55 antigen in biological samples. This target is a reported synonym of the PIK3R3 gene, which encodes phosphoinositide-3-kinase regulatory subunit 3. This protein is known to function in B cell differentiation and immune response pathways, among other biological roles. The human version of P55 has a canonical amino acid length of 461 residues and a protein mass of 54.4 kilodaltons, although 3 isoforms have been identified. It is reported to be widely expressed in many tissue types. P55 is a member of the PI3K p85 subunit protein family.