Human blood group system
P1PK (formerly: P) is a human blood group system (International Society of Blood Transfusion system 003) based upon the "A4GALT" gene on chromosome 22. The P antigen (later renamed P1) was first described by Karl Landsteiner and Philip Levine in 1927. The P1PK blood group system consists of three glycosphingolipid antigens: Pk, P1 and NOR. In addition to glycosphingolipids, terminal Galα1→4Galβ structures are present on complex-type N-glycans. The GLOB antigen (formerly P) is now the member of the separate GLOB (globoside) blood group system.
P1PK antigens.
The P1PK antigens are carbohydrate antigens that include Pk (Gb3), P1 and NOR1, NORint and NOR2. All are synthesized by Gb3/CD77 synthase (α1,4-galactosyltransferase, P1/Pk synthase).
The presence or absence of P1 antigen depends on the "A4GALT" transcript level. It was found that differential binding of transcription factors early growth response 1 (EGR1) and runt-related transcription factor 1 (RUNX1) to the SNP rs5751348 genomic region with the different genotypes in the "A4GALT" gene leads to differential activation of "A4GALT" expression, leading to two genotypes: P1 and P2.
P1PK phenotypes.
P1PK phenotypes are defined by reactivity to antibodies to anti-P1, anti-P, anti-Pk anti-PP1Pk. and anti-NOR antibodies.
P1PK antibodies.
Antibody detection.
Anti-P1Pk antibodies are not usually detected with routine laboratory methods. It is possible to detect them using the Donath-Landsteiner test. This test is performed on 2 vials of blood at two different temperatures: 4 °C and 37 °C (body temperature). A test is interpreted as positive only after a patient's red blood cells have been incubated at both temperatures and subsequently hemolyzed.