Abstract:
Introduction:
Kell blood group system, also known as the Kell system or Kell antigens, is one of the thirty-five known human blood group systems. The Kell system is named after Mrs. Kell, the patient in whom the antibodies were first discovered. The system is characterised by the presence or absence of antigens on the surface of red blood cells.
The Kell system is complex and consists of numerous antigens, with the most important being the K and k antigens. Individuals who possess the K antigen are referred to as K positive (K+), while those lacking the K antigen are referred to as K negative (K-). The K antigen is highly immunogenic, meaning that individuals lacking this antigen can develop antibodies against it if exposed to K+ blood.
The Kell blood group system is of particular importance in transfusion medicine and pregnancy management. If a person with K- blood is exposed to K+ blood through transfusion or pregnancy, they can develop antibodies against the K antigen. These antibodies can cause a severe immune reaction if the person receives another transfusion of K+ blood or if a fetus with K+ blood is carried by a mother with K- blood.
To determine a person's Kell blood type, laboratory tests are performed to detect the presence or absence of K and k antigens. This information is crucial for selecting compatible blood for transfusions and managing pregnancies to prevent complications.
It's important to note that the Kell blood group system is just one of many blood group systems, including the ABO system, Rh system, and numerous others. The combination of these systems determines an individual's complete blood type.
Nomenclature:
- Number of Kell antigens: 25
- ISBT symbol: KEL
- ISBT number: 006
- Gene symbol: KEL
- Gene name: Kell blood group
Basic Biochemistry and Common Phenotypes
The Kell blood group system is highly polymorphic, giving rise to numerous Kell antigens. Among them, the K and k antigens are of significant importance. These two major codominant allelic genes differ by a single amino acid and produce the K and k antigens, respectively. The k antigen is more prevalent in most populations. The K-k+ phenotype is found in 98% of Blacks and 91% of Caucasians.
Uncommon Phenotypes
The Kell system includes rare phenotypes, such as the Ko null phenotype and McLeod syndrome. Individuals with the Ko phenotype lack all Kell antigens but produce anti-Ku antibodies when exposed to RBCs expressing Kell antigens. McLeod syndrome, on the other hand, is characterized by weakly expressed Kell antigens and abnormal RBCs with spiky projections, leading to various systemic findings.
Expression of Kell Antigens
While Kell antigens were initially believed to be restricted to erythroid cells (RBCs and their precursors), recent research has shown their expression in myeloid tissues as well. In addition to blood cells, Kell antigens are expressed in small amounts on various organs, including lymphoid organs, cardiac and skeletal muscles, and the nervous system.
Functions of the Kell Glycoprotein
The Kell glycoprotein serves as an endothelin-3-converting enzyme, converting inactive endothelin-3 into active endothelin-3. This active form acts as a potent constrictor of blood vessels, highlighting the physiological significance of the Kell glycoprotein.
Clinical Significance of Kell Antibodies
Kell antibodies, particularly anti-Kell antibodies, can lead to transfusion reactions and hemolytic disease of the newborn. Transfusion reactions caused by anti-Kell antibodies can be severe, and the production of anti-Ku in individuals with the Ko phenotype has resulted in fatal hemolytic reactions. In HDN, maternal anti-Kell antibodies suppress the fetal production of red blood cells, leading to severe fetal anemia. Various other antibodies, such as anti-k, anti-Kpa, anti-Jsb, and others, have also been reported to cause HDN.
Molecular Information
The KEL gene, located on chromosome 7, is highly polymorphic and encodes the 25 Kell antigens. The Kell protein, composed of 732 amino acids, is glycosylated at multiple sites and anchored to the RBC membrane through a disulfide bond with the XK protein. Mutations in the KEL gene can result in different Kell blood group polymorphisms, impacting the antigenicity and expression of the Kell protein.
Conclusion
The Kell blood group system is a complex and diverse system with significant clinical implications. Understanding its history, nomenclature, basic biochemistry, phenotypes, antigen expression, functions of the Kell glycoprotein, and the clinical significance of Kell antibodies is crucial for effective transfusion medicine and the prevention of hemolytic disease of the newborn. Further research and advancements in this field will continue to enhance our understanding of the Kell blood group system and its role in human health.
