P Blood Group System

• P Blood Group System has an ISBT no. 003 with symbol P1PK and ISBT no. 028 with symbol GLOB
• P1PK has 3 antigens: P1, Pᵏ, and NOR
• GLOB has 2 antigens: P and PX2
• Antigens in P1PK System are structurally related to ABO antigens and exists as glycoproteins and glycolipids.
• P1 antigen expression is variable; P1 antigen is poorly developed at birth
• Anti-P1 is naturally occurring, cold-reacting, IgM antibodies.
• Anti-P1 is Often seen in individuals with P phenotype and optimally reactive at 4C
• Anti-P1 binds complement
• Anti-P1 does not cause HDN and rarely associated with HTR
• Anti-P1 reactivity can be inhibited in the presence of hydatid cyst fluid or P1 substance derived from pigeon eggs.
• Anti-P is IgM or IgM & IgG (clinically significant)
• Anti-P is naturally occurring individuals with P1k and P2k phenotypes.
• Anti-P is associated with recurrent spontaneous abortions
• Anti-P can trigger severe hemolytic transfusion reaction (HTR)
• Autoanti-P (Donath-Landsteiner antibody) is a cold-reacting IgG antibody associated with paroxysmal cold hemoglobinuria (PCH).
• An IgG autoantibody described as a biphasic hemolysin, since it can bind RBCs in the cold and via complement activation, the coated RBC lyse as they are warmed to 37C
• Autoanti-p (Donath-Landsteiner antibody) was demonstrated by Donath-Landsteiner test
• Anti-PP1Pk is IgM or IgM & IgG (clinically significant)
• Anti-PP1Pk is naturally occurring in P1 phenotype
• Anti-PP1Pk is associated with recurrent spontaneous abortion
• Anti-PP1Pk binds complement and may demonstrate in vitro hemolysis
• Anti-PP1Pk can cause severe hemolytic transfusion reaction (HTR)
• Anti-P1 is associated with parasitic infections
• Anti-PP1Pᵏ, Anti-P is associated with early abortions
• Auto anti-P is associated with Paroxysmal cold hemoglobinuria (PCH)
• P system antigens serves as receptor for P-fimbriated uropathogenic E.coli
• Pᵏ antigen is a receptor for Shiga toxins, which cause Shigella dysentery and E. coli associated hemolytic uremic syndrome (HUS)
• P antigen is a receptor of human parvovirus B19.
• Pᵏ recent studies shows that it provides some protection against HIV infection of peripheral blood mononuclear cells.