What are Antigens?
Antigen stands for Antibody Generator.Antigens are molecules that trigger an immune response which leads to the generation of antibodies depending on the type of the Antigen itself.
There are two types of Antigens; there are that are created by the human body depending on the person’s genetic code, this type is known as “Self Antigen“. A person’s immune system doesn’t attack his own self antigens. Another kind of antigens are those foreign to the body which the body is exposed to the surrounding environment, they are known as “Non-self Antigens“. The immune system is programmed to attack any object that has non-self antigens. In other words, the immune system can identify if a cell or a group of cells belong to the body or if they are foreign objects that must be fought against. And based on the type of antigens found within the object, the necessary types of White Blood Cells are created to treat the threat.
Human Lymphocyte/Leukocyte Antigens
Human Lymphocyte Antigens (HLAs) or Human Leukocyte Antigens are produced by human body according to the individual’s genetic characteristics. Human Lymphocyte Antigens can be found on the surface of all nucleated cells in human tissues.
Human Lymphocyte Antigens are found mostly on the White Blood Cells (Leukocytes), especially on the Lymphocytes where the HLAs are produced, which is the reason why the terms Human Leukocyte Antigens and Human Lymphocyte Antigen are used interchangeably to mean the same thing.
Types of Human Lymphocyte Antigens
Human Lymphocyte Antigens are produced by the body based on the genetic code found in Chromosome 6 of human DNA. Chromosome 6 contain different locus that encode different types Human Lymphocyte Antigens. These locus are HLA-A, HLA-B, HLA-C, HLA-DM, HLA-DOA, HLA-DOB, HLA-DP, HLA-DQ, and HLA-DR.
Human DNA is like a script that describes the features of our body. These features include eye color, hair color, nose shape, and so on. Each feature has different values like “Blue”, “Green”, “Brown”, and “Black” when it comes to the color or the eyes. In biology, the term “Allele” is used to mention the values of human featured stored in the DNA.
Human Lymphocyte Antigens are peptides that contain a short chain of amino acids. When the body produces peptides, it looks up the DNA for the peptide description. Each feature’s description is stored in a specific location within the DNA. In the case of Human Lymphocyte Antigens these locations are locus HLA-A, HLA-B, … etc that are found in chromosome 6. Depending on the individual’s genetics, the HLA locus present different HLA alleles for each individual the same way it represents a different eye color for each person. HLA alleles are presented by a number following the HLA type it belongs to. For example HLA-B1 and HLA-B2 are 2 different alleles defined by the HLA-B locus in chromosome 6.
Unfortunately, some of the HLA alleles are associated with or related diseases. For example, both of the HLA-DR3 and the HLA-DR4 are associated with Diabetes Mellitus Type 1. Since the body produces HLAs according to the persons genetic characteristics, these HLA associated conditions are considered as genetic disorders.
Major Histocompatibility Complex (MHC) is a group of molecules found on cell surface of all vertebrates to identify that the cell belongs to the vertebrate’s body and is not a foreign object that needs to be resisted by the vertebrate’s immune system.
The Major Histocompatibility Complex of a human is his own Human Lymphocyte Antigens. If the HLA found on a cell matches with the person’s DNA code for HLAs found in chromosome 6, this cell will be identified as a normal body cell and will not be attacked by the immune system. Otherwise, the cell, or any other object that doesn’t match with individual HLA complex, will be attacked by the immune system in order to protect the body from infections. Human Lymphocyte Antigen types A, B and C (HLA-A, HLA-B, HLA-C) are corresponding to MHC class I. MHC class II equivalents in human in HLA type D (DM, DOA, DOB, DP, DQ, and DR) and MHC class III equivalent in human is the Immune Complement System.
When it comes to organ transplant, a histocompatibility test need to be performed on both of the donor and the recipient to ensure that the recipient’s body will not attack the transplanted organ or tissues or to minimize the chances of activating an immune response against the new comer. This histocompatibility check is done by examining the donor’s HLA complex to be sure that is it compatible with the recipient’s HLAs. For example if both the donor have the same exact HLA alleles for each HLA type, that would make the donor pass the MHC check. Depending on the condition and the type of the organ to be transplanted, further compatibility examinations may be required.