Kidd antigen system
The Kidd antigen system is a classification method for blood typing that focuses on specific proteins, known as Kidd blood antigens, found on the surface of red blood cells. This system is particularly significant in forensic science, as the variability of these antigens among individuals can facilitate the identification of blood samples left at crime scenes. Each red blood cell can carry a multitude of antigens, and even a small drop of blood can contain millions of these cells, making the Kidd system a valuable tool for forensic analysis.
The Kidd antigen, specifically, is involved in transporting urea and is linked to kidney function, encoded by the Jk gene located on chromosome 18. There are two primary alleles of this gene, Jka and Jkb, resulting in various combinations of Kidd antigen expression. When mismatched blood transfusions occur, or in cases where a pregnant woman has antibodies against a Kidd antigen present in her fetus, health complications may arise, such as hemolytic disease of the newborn. The system categorizes individuals into four distinct antigen combinations, which enhances its utility in forensic investigations, especially when combined with other blood typing systems like ABO. Advances in genetic technology have further refined the accuracy of Kidd antigen testing, aiding law enforcement in narrowing down suspect pools based on blood evidence.
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Kidd antigen system
DEFINITION: System used for typing blood based on specific proteins, known as Kidd blood antigens, on the surface of red blood cells.
SIGNIFICANCE: Because Kidd blood antigens are present on red blood cells in forms that vary from person to person, these differences can aid in the identification of blood left at crime scenes.
A drop of blood the size of a pinhead can contain five million red blood cells. Each red blood cell has up to one hundred different surface molecules that show some person-to-person variation. Such a cadre of molecules, otherwise known as antigens, provides the forensic scientist with a large resource for identifying the owner of a bloodstain at a crime scene.
After blood dries, the red blood cells explode, and this complicates blood type analysis because many blood-borne molecules are unstable when dried. For this reason, the forensic laboratories of the Federal Bureau of Investigation (FBI) typically test only for the ABO, rhesus (Rh), and Lewis blood group antigens in dried blood. However, some specific blood proteins are present in dried blood and can be used for blood type analysis.
Red blood cell surface proteins regulate the entry and egress of various molecules. One particular protein on the surface of red blood cells is called the Kidd or Jk antigen. This protein transports a nitrogen-based waste product called urea from the cell and is also found in the kidney. The Kidd antigen is encoded by the Jk (or SCL14A1/HUT11) gene, which is located on chromosome 18. The Jk gene comes in two main functional forms (alleles), Jka and Jkb. The bodies of persons who lack a functional Kidd antigen protein (Jka–b–) are unable to concentrate urine properly. F. H. Allen and his colleagues first described the Kidd blood grouping system in 1951.
Because humans have two copies of each chromosome, they can possess two copies of Jka, two copies of Jkb, or one copy of Jka and another copy of Jkb. An individual with two copies of Jkb who receives a blood transfusion from a donor who possesses two copies of Jka can form antibodies against the Jka form of the Kidd antigen, and this prevents the individual from tolerating a second blood transfusion from a donor who possesses a copy of Jka. Similarly, if a pregnant woman has antibodies against a particular Kidd antigen that is present on the red blood cells of her unborn baby, these maternal antibodies can destroy the fetal red blood cells and cause hemolytic disease of the newborn (HDN).
Because individuals can have one of four distinct combinations of Kidd antigens—Jk(a+ b–), Jk(a– b+), Jk(a+ b+), and Jk(a– b–)—Kidd antigens are useful for typing blood found at crime scenes, especially when this system is used in combination with other blood group systems (such as ABO, Duffy, or MN). Identification of the types of blood found at crime scenes may enable law-enforcement investigators to narrow their search for suspects. Technological and scientific improvements made in the field of genetics in the 2010s and early 2020s have allowed scientists to gain more accurate results through the study of Kidd antigens.
Bibliography
Gueuning, Morgan, et al. "Resolving Genotype–Phenotype Discrepancies of the Kidd Blood Group System Using Long-Read Nanopore Sequencing." Biomedicines, vol. 12, no. 1, 19 Jan. 2024, doi.org/10.3390/biomedicines12010225-logo. Accessed 16 Aug. 2024.
Nash, Jay Robert. Forensic Serology. New York: Chelsea House, 2006.
Nordby, Jon J. Dead Reckoning: The Art of Forensic Detection. Boca Raton, Fla.: CRC Press, 2000.
Platt, Richard. Crime Scene: The Ultimate Guide to Forensic Science. New York: Dorling Kindersley, 2003.