All the living cells in the human body require a constant supply of nutrients, oxygen and other essential substances. Also for the healthy functioning of the body and the tissues, the wasteful substances needed to be removed constantly. Therefore a mechanism is a must that helps in transporting nutrients and other substances from one cell to another. In simple organisms, water is present as a means of transport. But in complex organisms, blood is the commonly used body fluid. The lymph can also serve special purposes in transporting some nutrients. As blood is present in human beings, this blood in every individual is not the same. It has certain factors that make the blood different. This helps in forming blood groups. Based on these factors there is a P blood group system, Globoside blood group system, ABO blood group system, and the clinical significance of P blood group system. To study all these, firstly we need to clearly understand blood.

Blood

It is specialized connective tissue. It consists of a fluid matrix, plasma and also has formed elements that form the cellular portion. Plasma makes 55% of the blood and the rest 45% is made up of formed elements. Plasma is the fluid that forms the matrix of the blood. It is straw coloured. The plasma is composed of water, proteins, minerals and other amino acids. The water makes 90% of the plasma. Fibrinogen, globulin and albumins are the proteins that are present in plasma. Fibrinogen helps in the clotting of blood. Globulins help in the defence mechanism of the body and albumins help to maintain the osmotic balance. Glucose, amino acids and lipids are also present in the plasma and these substances enter and leave the plasma at regular intervals. The formed elements that make the rest of the composition are erythrocytes, leukocytes and platelets. Erythrocytes are the red blood cells that give blood its red colour and also help in transporting oxygen from one cell to another. The leukocytes are the white blood cells and they are known as soldiers of the body. They are named so because they help in fighting the body with infections. The leukocytes are lymphocytes, monocytes, eosinophils, basophils and neutrophils. The platelets in the blood are colourless and non-nucleated fragments of the cells. They are produced by the bone marrow and help in blood clotting.

Blood Group

Antigens are the molecules that are present on the surface of cells and thus they are recognised as foreign cells by the immune system and thus they can induce an immune response. To counter these antigens, the human body produces certain chemicals to fight against them and destroy them. These are known as antibodies. They get bonded to the antigens in a special fashion. The membranes of the red blood cells also contain some antigens. The ABO and RH- blood grouping is done on this basis only. These two along with the p blood group system and globoside blood group system are used all over the world.

P Blood Group System

This is also known as the p1pk blood group system. It is based on the A4GALT gene on chromosome number 22. Karl Landsteiner and Levine were the first ones that described the P antigen and later named it P1. This p blood group system consists of three glycosphingolipid antigens that are P1, NOR and Pk. The GLOB antigen that was formerly part of the P blood group system is now a part of the globoside blood group system. The antigens of the P blood group system are carbohydrate antigens that include GB3, P1, NOR1 and NOR2. These all are synthesized by GB3 synthase. The Pk antigen is a receptor of Shinga toxins. This toxin is produced by the Shigella dysenteriae. Some strains are also produced by Escherichia coli. These strains of Escherichia coli can cause the hemolytic uremic syndrome. The P1, P and LKE antigens, these all serve as receptors for P-fimbriated uropathogenic. This can further cause chronic urinary tract infections. P1 antigens presence or absence depends on A4GALT transcript levels. The differential binding of the transcription factors EGR1 and runt-related transcription factor1(RUNX1) to the SNP rs5751348 genomic region with different genotypes in the A4GALT gene leads to differential activation of A4GALT expression. The phenotypes of the P1PK are defined by their reactivity to the antibodies to anti-P1, anti-P and anti-NOR antibodies.

P1 phenotype: Anti-P1(+), anti-P(+) and anti-Pk(-). They are found in 95% blacks and 30% Japanese.
P2 phenotype: Anti-P1(-), anti-P(+). It is found in 5% of blacks.
Rare NOR phenotype: NOR1 and NOR2 glycosphingolipid antigens cause this.

The antiP1Pk antibodies are not detected in laboratory methods. They are detected by Donath- Landsteiner test. In this test, two blood vials are taken at different temperatures. The interpretations are made only when the patient's red blood cells are incubated at both the temperatures and then hemolyzed.

[Image: P blood Group System]

Globoside Blood Group System

Globoside has more than one sugar and it is a type of glycosphingolipid. The sugar is present as the side chain of ceramide. The sugars are a combination of D-glucose, D-galactose and N-acetylgalactosamine. When it has only one sugar then it is known as cerebroside. Glycosidases can help to cleave away the side chain. Fabry’s disease is caused by the deficiency of galactosidase-A. This is a metabolic disease that is caused by the accumulation of globotriaosylceramide. Glycolipid and antigen-p are the structures present in this blood group.

ABO Grouping

Karl Landsteiner gave this system in 1901. This blood group is based on the presence and absence of two surface antigens which are A and B and are present on the RBC. The individual plasma also contains anti-A and anti-B antibodies. According to him, if an antigen is present in the blood then its corresponding antibody will be present in the individual. Also, if the antigen is absent in the RBC, then the antibody must be present in the plasma. To its own antigens of red blood cells, the immune system exhibits tolerance. So a person who has A blood group will have B antibodies and not A-antibodies. The same applies to the B blood group. For the AB blood group, no antibodies are produced and for the O-blood group, both the antibodies that are anti-A and anti-B are present.

Rh Grouping

Rh factors are another group of antigens that are found on the red blood cells. People that possess Rh antigens are known as Rh-positive and the ones that do not have these antigens are known as Rh-negative. Rh-positive and Rh-negative blood groups cannot be mixed together as they will produce antibodies against each other and make the blood clot.

Clinical Significance of P Blood Group System

The clinical significance of p blood group system are:

The accurate grouping of blood will help in the process of blood transfusion.
It can be used in the treatment of blood cancer.
Packed blood samples can be stored and used in cases of emergency such as an accident when a lot of blood leaks.
Proper blood grouping can help in the safe birth of a child.

Conclusion

We can conclude that blood is a very important fluid in our body. It helps in transporting nutrients and oxygen to all the cells of the body. Blood also has platelets that help in blood clotting. Red blood cells present in the blood transports oxygen and also gives the red colour to the blood. The white blood cells help in fighting infections and foreign particles. The system of blood grouping is based on different antigens present on the red blood cells. The P blood group system has P1, p-NOR and Pk antigens.

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FAQs on Understand the P Blood Group System in Biology

1. What is the P blood group system?

The P blood group system is a classification of human blood based on the presence or absence of specific carbohydrate antigens on the surface of red blood cells. These antigens, primarily P1, P, and Pk, are glycosphingolipids. Discovered in 1927 by Landsteiner and Levine, this system is clinically significant in blood transfusion and is distinct from the more commonly known ABO and Rh systems.

2. What are the key antigens and antibodies of the P1PK system?

The P1PK blood group system is defined by three main antigens and their corresponding antibodies. The primary components are:

Antigens: These are carbohydrate structures on the red blood cell surface. The main ones are P1, P, and Pk. An individual's phenotype is determined by which of these antigens they express.
Antibodies: These are proteins found in the plasma. The most common antibody is anti-P1, found in individuals with the P2 phenotype. Rarer, more potent antibodies include anti-P and the clinically significant anti-PP1Pk, found in individuals with the rare p (P null) phenotype.

3. What are the common phenotypes in the P blood group system?

The two most common phenotypes in the P blood group system are:

P1: Individuals have both P1 and P antigens on their red blood cells. This is the most frequent phenotype, occurring in approximately 80% of Caucasians and 95% of Black individuals.
P2: Individuals have only the P antigen on their red blood cells and naturally produce the anti-P1 antibody in their plasma.

Much rarer phenotypes include P1k, P2k, and the p (or P null) phenotype, which lacks all P system antigens.

4. How rare are the P blood group phenotypes?

The rarity of P blood group phenotypes varies significantly. The P1 phenotype is very common, found in about 4 out of 5 people in many populations. The P2 phenotype is less common but still prevalent. However, the p (P null) and Pk phenotypes are extremely rare, with an incidence estimated to be around 1 in 200,000 to 1 in a million people, making them some of the rarest blood types globally.

5. What is the clinical significance of the P blood group system?

The P blood group system is clinically important for several reasons. The antibody anti-P1 is usually a cold-reacting antibody and rarely causes transfusion issues. However, the antibody anti-PP1Pk, produced by individuals with the rare p (P null) phenotype, is a potent hemolysin that can cause severe hemolytic transfusion reactions and has been associated with recurrent spontaneous abortions in pregnancy. Additionally, autoanti-P is the antibody responsible for the biphasic hemolysis seen in Paroxysmal Cold Hemoglobinuria (PCH).

6. How does the rare P null (p) phenotype differ from the Pk phenotype?

The P null (p) and Pk phenotypes are both rare but differ biochemically and immunologically. Individuals with the P null (p) phenotype lack all antigens of the P system (P, P1, and Pk). Their bodies therefore produce a strong antibody called anti-PP1Pk. In contrast, individuals with the Pk phenotype express the Pk antigen but lack the P antigen. They typically produce anti-P. This difference is crucial for blood transfusion, as the antibodies produced by each group will react against different sets of antigens.

7. How is the P blood group system related to infectious diseases?

The P blood group antigens serve as functional cell surface receptors for various pathogens, which explains their importance beyond transfusion medicine. For example, the P antigen is the cellular receptor for human parvovirus B19, the virus that causes fifth disease. Furthermore, the Pk antigen acts as a receptor for the Shiga toxins produced by certain strains of E. coli, linking it to the severity of hemolytic-uremic syndrome (HUS).