The Ii antigen system is a human blood group system based upon a gene on chromosome 6 and consisting of the I antigen and the i antigen. [1] The I antigen is normally present on the cell membrane of red blood cells in all adults, while the i antigen is present in fetuses and newborns. [2]
Adult red blood cells express I antigen abundantly. [3] Developing fetuses and newborns express i antigen until around 13-20 months after birth, when I antigen starts to be expressed instead. [3] Like ABH antigens, which make up the ABO blood group, I and i antigens are not restricted to the red blood cell membrane, but are found on most human cells and in body fluids such as saliva. [1]
The I and i antigens are carbohydrate structures composed of repeating units of N-acetyllactosamine (LacNAc), and are located on the interior of structures carrying ABH and Lewis antigens. [1] [3] LacNAc repeats are made by the enzymes B3GNT1 and B4GALT1. [4] The i antigen is made of linear repeats, while the structure of the I antigen is branched. [3] Unlike most other blood groups, the two antigens are not encoded by different alleles; rather, I-branching enzyme converts i antigen to I antigen by adding branches. [5] [6] The gene encoding I-branching enzyme is located on chromosome 6. [6]
The function of I and i antigens are unknown but may be related to hematopoiesis, the production of blood. [6] The rapid conversion from i to I antigens after birth suggests that I antigen plays an important role in adult red blood cells. [3] The presence of the linear i antigen in fetuses, rather than the branched I antigen, may have developed as an evolutionary mechanism to prevent ABO hemolytic disease of the fetus and newborn. [1] Enhanced expression of i antigen is associated with conditions involving stress hematopoiesis such as leukemia and sickle cell disease. [7]
Transient autoantibodies against I antigen are common, especially after infection by Mycoplasma pneumoniae , and are rarely significant except in cold agglutinin disease. [1] Transient antibodies against i antigen are common after infectious mononucleosis and are also not clinically significant. [1] Antibodies which recognize both I and i antigens are termed anti-j antibodies. [1]
The autoantibodies involved in cold agglutinin disease are usually against I antigen. [8] The antibodies are usually IgM (kappa subtype), unlike transient autoantibodies which are generally IgG. [1] Cold-reactive IgM antibodies (cold agglutinins) bind to I antigen on red blood cells, and unlike IgG, are able to cause agglutination of red blood cells and activate complement to cause hemolysis, leading to anemia. [1] [8]
Rarely, individuals have the i antigen on their red blood cells into adulthood, known as the adult i phenotype. [1] This is due to the presence of a mutation in the GCNT2 gene which encodes the I-branching enzyme. [1] [3] These individuals have alloantibodies against the I antigen, though these are typically cold agglutinins and are unlikely to cause transfusion reactions. [2] [9]
The adult i phenotype is associated with congenital cataracts, most markedly in Japanese and Taiwanese people and least markedly in Caucasian people. [1] [6] Cataracts occur when i antigen rather than I antigen is present on the epithelium of the lens, due to a mutation in the form of the I-branching enzyme which is expressed in lens epithelium, IGNTB. [10]
The adult i phenotype is inherited in a recessive manner. [1]
The I antigen was first described in 1956 and the i antigen was discovered in 1960. [1] I and i were the first discovered antigens which change significantly during human development. [4] The letter I was chosen to reflect the "individuality" of a person studied who lacked the I antigen. [6]
A similar blood group system with a developmental change resembling the Ii system (with human neonatal cells expressing i antigen and adult cells expressing I antigen) has been observed in most primates, including chimpanzees and monkeys. [1] This is not seen in non-primates: cats, dogs, or guinea pigs. [1]
The direct and indirect Coombs tests, also known as antiglobulin test (AGT), are blood tests used in immunohematology. The direct Coombs test detects antibodies that are stuck to the surface of the red blood cells. Since these antibodies sometimes destroy red blood cells they can cause anemia; this test can help clarify the condition. The indirect Coombs test detects antibodies that are floating freely in the blood. These antibodies could act against certain red blood cells; the test can be carried out to diagnose reactions to a blood transfusion.
The ABO blood group system is used to denote the presence of one, both, or neither of the A and B antigens on erythrocytes. For human blood transfusions, it is the most important of the 44 different blood type classification systems currently recognized by the International Society of Blood Transfusions (ISBT) as of December 2022. A mismatch in this, or any other serotype, can cause a potentially fatal adverse reaction after a transfusion, or an unwanted immune response to an organ transplant. The associated anti-A and anti-B antibodies are usually IgM antibodies, produced in the first years of life by sensitization to environmental substances such as food, bacteria, and viruses.
Autoimmune hemolytic anemia (AIHA) occurs when antibodies directed against the person's own red blood cells (RBCs) cause them to burst (lyse), leading to an insufficient number of oxygen-carrying red blood cells in the circulation. The lifetime of the RBCs is reduced from the normal 100–120 days to just a few days in serious cases. The intracellular components of the RBCs are released into the circulating blood and into tissues, leading to some of the characteristic symptoms of this condition. The antibodies are usually directed against high-incidence antigens, therefore they also commonly act on allogenic RBCs. AIHA is a relatively rare condition, with an incidence of 5–10 cases per 1 million persons per year in the warm-antibody type and 0.45 to 1.9 cases per 1 million persons per year in the cold antibody type. Autoimmune hemolysis might be a precursor of later onset systemic lupus erythematosus.
Paroxysmal cold hemoglobinuria (PCH) or Donath–Landsteiner hemolytic anemia (DLHA) is an autoimmune hemolytic anemia featured by complement-mediated intravascular hemolysis after cold exposure. It can present as an acute non-recurrent postinfectious event in children, or chronic relapsing episodes in adults with hematological malignancies or tertiary syphilis. Described by Julius Donath (1870–1950) and Karl Landsteiner (1868–1943) in 1904, PCH is one of the first clinical entities recognized as an autoimmune disorder.
The Kell antigen system is a human blood group system, that is, a group of antigens on the human red blood cell surface which are important determinants of blood type and are targets for autoimmune or alloimmune diseases which destroy red blood cells. The Kell antigens are K, k, Kpa, Kpb, Jsa and Jsb. The Kell antigens are peptides found within the Kell protein, a 93-kilodalton transmembrane zinc-dependent endopeptidase which is responsible for cleaving endothelin-3.
The Kidd antigen system are proteins found in the Kidd's blood group, which act as antigens, i.e., they have the ability to produce antibodies under certain circumstances. The Jk antigen is found on a protein responsible for urea transport in the red blood cells and the kidney. They are important in transfusion medicine. People with two Jk(a) antigens, for instance, may form antibodies against donated blood containing two Jk(b) antigens. This can lead to hemolytic anemia, in which the body destroys the transfused blood, leading to low red blood cell counts. Another disease associated with the Jk antigen is hemolytic disease of the newborn, in which a pregnant woman's body creates antibodies against the blood of her fetus, leading to destruction of the fetal blood cells. Hemolytic disease of the newborn associated with Jk antibodies is typically mild, though fatal cases have been reported.
The Rh blood group system is a human blood group system. It contains proteins on the surface of red blood cells. After the ABO blood group system, it is the most likely to be involved in transfusion reactions. The Rh blood group system consisted of 49 defined blood group antigens in 2005. As of 2023, there are over 50 antigens among which the five antigens D, C, c, E, and e are the most important. There is no d antigen. Rh(D) status of an individual is normally described with a positive (+) or negative (−) suffix after the ABO type. The terms Rh factor, Rh positive, and Rh negative refer to the Rh(D) antigen only. Antibodies to Rh antigens can be involved in hemolytic transfusion reactions and antibodies to the Rh(D) and Rh antigens confer significant risk of hemolytic disease of the newborn.
hh, or the Bombay blood group, is a rare blood type. This blood phenotype was first discovered in Bombay by Dr. Y. M. Bhende in 1952. It is mostly found in the Indian sub-continent and Iran.
P1PK is a human blood group system based upon the A4GALT gene on chromosome 22. The P antigen was first described by Karl Landsteiner and Philip Levine in 1927. The P1PK blood group system consists of three glycosphingolipid antigens: Pk, P1 and NOR. In addition to glycosphingolipids, terminal Galα1→4Galβ structures are present on complex-type N-glycans. The GLOB antigen is now the member of the separate GLOB (globoside) blood group system.
The Lutheran antigen systems is a classification of human blood based on the presence of substances called Lutheran antigens on the surfaces of red blood cells. There are 19 known Lutheran antigens. The name Lutheran stems from a blood donor's misspelled last name, reportedly named Lutteran or Luteran. All of these antigens arise from variations in a gene called BCAM. The system is based on the expression of two codominant alleles, designated Lua and Lub. The antigens Aua and Aub, known as the Auberger antigens, were once thought to make up a separate blood group but were later shown to be Lutheran antigens arising from variations in the BCAM gene.
The Lewis antigen system is a human blood group system. It is based upon two genes on chromosome 19: FUT3, or Lewis gene; and FUT2, or Secretor gene. Both genes are expressed in glandular epithelia. FUT2 has a dominant allele which codes for an enzyme and a recessive allele which does not produce a functional enzyme. Similarly, FUT3 has a functional dominant allele (Le) and a non-functional recessive allele (le).
Secretor status refers to the presence or absence of water-soluble ABO blood group antigens in a person's bodily fluids, such as saliva, tears, breast milk, urine, and semen. People who secrete these antigens in their bodily fluids are referred to as secretors, while people who do not are termed non-secretors. Secretor status is controlled by the FUT2 gene, and the secretor phenotype is inherited in an autosomal dominant manner, being expressed by individuals who have at least one functioning copy of the gene. The non-secretor phenotype (se) is a recessive trait. Approximately 80% of White people are secretors, while 20% are non-secretors. Non-secretors have reduced susceptibility to the most common strains of norovirus. Expression of the antigens in the Lewis blood group is also affected by secretor status: non-secretors cannot produce the Le(b) antigen.
Cold sensitive antibodies (CSA) are antibodies sensitive to cold temperature. Some cold sensitive antibodies are pathological and can lead to blood disorder. These pathological cold sensitive antibodies include cold agglutinins, Donath–Landsteiner antibodies, and cryoglobulins which are the culprits of cold agglutinin disease, paroxysmal cold hemoglobinuria in the process of Donath–Landsteiner hemolytic anemia, and vasculitis, respectively.
The Vel blood group is a human blood group that has been implicated in hemolytic transfusion reactions. The blood group consists of a single antigen, the high-frequency Vel antigen, which is expressed on the surface of red blood cells. Individuals are typed as Vel-positive or Vel-negative depending on the presence of this antigen. The expression of the antigen in Vel-positive individuals is highly variable and can range from strong to weak. Individuals with the rare Vel-negative blood type develop anti-Vel antibodies when exposed to Vel-positive blood, which can cause transfusion reactions on subsequent exposures.
The Junior blood group system is a human blood group defined by the presence or absence of the Jr(a) antigen, a high-frequency antigen that is found on the red blood cells of most individuals. People with the rare Jr(a) negative blood type can develop anti-Jr(a) antibodies, which may cause transfusion reactions and hemolytic disease of the newborn on subsequent exposures. Jr(a) negative blood is most common in people of Japanese heritage.
Blood compatibility testing is conducted in a medical laboratory to identify potential incompatibilities between blood group systems in blood transfusion. It is also used to diagnose and prevent some complications of pregnancy that can occur when the baby has a different blood group from the mother. Blood compatibility testing includes blood typing, which detects the antigens on red blood cells that determine a person's blood type; testing for unexpected antibodies against blood group antigens ; and, in the case of blood transfusions, mixing the recipient's plasma with the donor's red blood cells to detect incompatibilities (crossmatching). Routine blood typing involves determining the ABO and RhD type, and involves both identification of ABO antigens on red blood cells and identification of ABO antibodies in the plasma. Other blood group antigens may be tested for in specific clinical situations.
The Lan blood group system is a human blood group defined by the presence or absence of the Lan antigen on a person's red blood cells. More than 99.9% of people are positive for the Lan antigen. Individuals with the rare Lan-negative blood type, which is a recessive trait, can produce an anti-Lan antibody when exposed to Lan-positive blood. Anti-Lan antibodies may cause transfusion reactions on subsequent exposures to Lan-positive blood, and have also been implicated in mild cases of hemolytic disease of the newborn. However, the clinical significance of the antibody is variable. The antigen was first described in 1961, and Lan was officially designated a blood group in 2012.
The Sid blood group system is a human blood group defined by the presence or absence of the Sd(a) antigen on a person's red blood cells. About 96% of people are positive for the Sd(a) antigen, which is inherited as a dominant trait. Among Sd(a) positive individuals, the expression of the antigen ranges from extremely weak to extremely strong. Very strong expression of the antigen is referred to as a Sd(a++) phenotype. In addition to being expressed on red blood cells, Sd(a) is secreted in bodily fluids such as saliva and breast milk, and is found in the highest concentrations in urine. Urine testing is considered the most reliable method for determining a person's Sid blood type.
The Augustine blood group system is a human blood group system. It includes four red blood cell surface glycoprotein antigens which are encoded by alleles of the gene SLC29A1.
An antibody elution is a clinical laboratory diagnostic procedure which removes sensitized antibodies from red blood cells, in order to determine the blood group system antigen the antibody targets. An antibody elution is deemed necessary when antibodies of the immunoglobulin class G (IgG) are found sensitized (bound) to peripheral red cells collected from a blood product transfusion recipient. IgG antibodies are detected using an assay known as the direct antiglobulin test.
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