HUMAN LEUKOCYTE ANTIGENS (HLA)

INTRODUCTION:  Human leukocyte antigens (HLA) are antigens on White Blood Cells that are representative of the antigens present on all the cells of an individual.  Leukocytes  These are our “self” antigens that identify cells that belong in the body. Recall that in the ABO blood group of Red Blood Cells, there are only two antigens, A and B, and four possible types: A, B, AB, and O. The ABO blood grouping:  Red blood cells:  HLA antigens are also given letter names. HLA A, B, and C are called class I proteins, with from 100 to more than 400 possibilities for the specific protein each can be. The several class II proteins are given various D designations and, again, there are many possibilities for each. Each person has two genes for each HLA type, because these types are inherited, just as RBC types are inherited.

DIFFERENCES IN HLA:  Members of the same family may have some of the same HLA types, and identical twins have exactly the same HLA types. The purpose of the HLA types is to provide a “self” comparison for the immune system to use when pathogens enter the body. The T lymphocytes compare the “self” antigens on macrophages to the antigens on bacteria and viruses. Because these antigens do not match ours, they are recognized as foreign; this is the first step in the destruction of a pathogen.

HLA AND ORGAN TRANSPLANTS:  The surgical transplantation of organs has also focused on the HLA. The most serious problem for the recipient of a transplanted heart or kidney is rejection of the organ and its destruction by the immune system. You may be familiar with the term tissue typing. This process involves determining the HLA types of a donated organ to see if one or several will match the HLA types of the potential recipient. If even one HLA type matches, the chance of rejection is lessened. Although all transplant recipients (except corneal) must receive immunosuppressive medications to prevent rejection, such medications make them more susceptible to infection.  The closer the HLA match of the donated organ, the lower the dosage of such medications, and the less chance of serious infections.  

HLA AND AUTOIMMUNITY:  Sometimes a virus enters the body and stimulates the immune system to produce antibodies. The virus is destroyed, but one of the person’s own antigens is so similar to the viral antigen that the immune system continues its activity and begins to destroy this similar part of the body.  This is a scenario known as autoimmunity.  Autoimmunity  Another possibility is that a virus damages a self-antigen to the extent that it is now so different that it will be perceived as foreign. These are two theories of how autoimmune diseases are triggered, which is the focus of much research in the field of immunology.  

RELATED;

1.  AUTOIMMUNE DISEASES

2. MAJOR HISTOCOMPATIBILITY COMPLEX

3. REFERENCES