The term HLA refers to the Human Leukocyte Antigen System, which is controlled by genes on the short arm of chromosome six. The HLA loci are part of the genetic region known as the major histocompatibility complex (MHC).
The MHC has genes (including HLA) that form part of the normal function of the immune response. The essential role of the HLA antigens lies in the control of self-recognition and thus defense against microorganisms. The HLA loci, by virtue of their extreme polymorphism, ensure that few individuals are identical and thus the population at large is well equipped to deal with attacks. Because some HLA antigens are recognized on all body tissues (rather than just blood cells), the identification of HLA antigens is described as “Tissue typing”.
In the last twenty years, there has been an exponential growth in the application of DNA technology to the field of Histocompatibility and Immunogenetics. The development and application of several different DNA methods by many laboratories have resulted in that nearly every Histocompatibility and Immunogenetics laboratory performs some DNA typing to detect HLA alleles.
The human leukocyte antigen system (HLA) is the name of the major histocompatibility complex
(MHC) in humans. The super locus contains a large number of genes related to immune system
function in humans. This group of genes is located on chromosome 6 and encodes cell-surface
antigen-presenting proteins and many other genes. The HLA genes are the human versions of the
major histocompatibility complex (MHC) genes that are found in most vertebrates and are the
best studied of the MHC genes. The proteins encoded by certain genes are also known as
antigens, as a result of their historic discovery as factors in organ transplantations. The major HLA
antigens are essential elements in immune function. Different classes have different functions.
HLA class I antigens (A, B & C) present peptides from inside the cell (including viral peptides if
present). These peptides are produced from digested proteins that are broken down in the
proteasomes. The peptides are generally small polymers, about 9 amino acids in length. Foreign
antigens attract killer T-cells (also called CD8 positive cells) that destroy cells.
HLA class II antigens (DP, DQ, & DR) present antigens from outside the cell to T-lymphocytes.
These particular antigens stimulate T-helper cells to reproduce, and these T-helper cells then
stimulate antibody-producing B-cells. Self-antigens are suppressed by suppressor T-cells.