P antigen system

P antigens

• P^k antigen is a receptor for shiga toxins and Escherichia coli-associated hemolytic uremic syndrome. It is also a receptor for Streptococcus suis.
• The P antigen is a receptor for parvovirus B19.
• P1, P, P^k and LKE antigens all serve as receptors for P-fimbriated uropathogenic E. coli.

  P phenotypes

• P₁ Phenotype: anti-P₁, anti-P and anti-PP₁P^k and anti-P^k. Seen in 95% of Blacks and 80% of Whites.
• P2 Phenotype: anti-P₁, anti-P, antiPP₁P^k, and anti-P^k. Seen in 5% of Blacks and 20% of Whites.
• Rare p phenotype : anti-P₁, anti-P, anti-PP₁P^k, and anti-P^k. These individuals have a very strong anti-PP₁P^k which can be associated with delayed hemolytic transfusion reactions and hemolytic disease of the fetus and newborn.

  P antibodies

• Anti-P1 titers are often elevated in patients with liver flukes, hydatid cyst disease and who are frequently exposed to birds.
• Anti-PP1P^k is composed of a mixture of anti-P, anti-P1 and antiP^k in the serum of p individuals. Alloanti-P is seen in the sera of P₁^k and P₂^k persons and is naturally occurring and predominantly IgM isotype. The antibodies are capable of causing hemolytic transfusion reactions and hemolytic disease of the fetus and newborn. There is a relationship between anti-PP1P^k and early spontaneous abortion.
• Autoanti-P is an autoantibody of P specificity and is seen in individuals with paroxysmal cold hemoglobinuria. In PCH, autoanti-P is of IgG isotype and is a biphasic hemolysin. In the body, autoanti-P antibodies bind to red blood cells at cold temperatures and, after circulating back to the core of the body, subsequently induce intravascular hemolysis in warmer temperatures.

  Antibody detection