HLA-G
Encyclopedia
HLA-G histocompatibility antigen, class I, G, also known as human leukocyte antigen G (HLA-G), is a protein
that in humans is encoded by the HLA-G gene
.
HLA-G belongs to the HLA
nonclassical class I heavy chain paralogues. This class I molecule is a heterodimer consisting of a heavy chain and a light chain (beta-2 microglobulin
). The heavy chain is anchored in the membrane. HLA-G is expressed on fetal derived placental cells. The heavy chain is approximately 45 kDa and its gene contains 8 exons. Exon one encodes the leader peptide, exons 2 and 3 encode the alpha1 and alpha2 domain, which both bind the peptide, exon 4 encodes the alpha3 domain, exon 5 encodes the transmembrane region, and exon 6 encodes the cytoplasmic tail.
, being expressed in the placenta
, while the classical MHC class I
genes HLA-A
and HLA-B
are not.
The presence of soluble HLA-G (sHLA-G) in embryos is associated with better pregnancy rate
s. In order to optimize pregnancy rate
s, there is significant evidence that a morphological scoring system is the best strategy for the selection of embryos. However, presence of soluble HLA-G might be considered as a second parameter if a choice has to be made between embryos of morphologically equal quality.
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
that in humans is encoded by the HLA-G gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
.
HLA-G belongs to the HLA
Human leukocyte antigen
The human leukocyte antigen system is the name of the major histocompatibility complex in humans. The super locus contains a large number of genes related to immune system function in humans. This group of genes resides on chromosome 6, and encodes cell-surface antigen-presenting proteins and...
nonclassical class I heavy chain paralogues. This class I molecule is a heterodimer consisting of a heavy chain and a light chain (beta-2 microglobulin
Beta-2 microglobulin
β2 microglobulin also known as B2M is a component of MHC class I molecules, which are present on all nucleated cells . In humans, the β2 microglobulin protein is encoded by the B2M gene.-Structure and function:...
). The heavy chain is anchored in the membrane. HLA-G is expressed on fetal derived placental cells. The heavy chain is approximately 45 kDa and its gene contains 8 exons. Exon one encodes the leader peptide, exons 2 and 3 encode the alpha1 and alpha2 domain, which both bind the peptide, exon 4 encodes the alpha3 domain, exon 5 encodes the transmembrane region, and exon 6 encodes the cytoplasmic tail.
Function
HLA-G may play a role in Immune tolerance in pregnancyImmune tolerance in pregnancy
Immune tolerance in pregnancy or gestational/maternal immune tolerance is the absence of a maternal immune response against the fetus and placenta, which thus may be viewed as unusually successful allografts, since they genetically differ from the mother. In the same way, many cases of spontaneous...
, being expressed in the placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
, while the classical MHC class I
MHC class I
MHC class I molecules are one of two primary classes of major histocompatibility complex molecules and are found on every nucleated cell of the body...
genes HLA-A
HLA-A
HLA-A are a group of human leukocyte antigens that are encoded by the HLA-A locus on human chromosome 6p. The HLA genes constitute a large subset of the Major histocompatibility complex of humans. HLA-A is a component of certain MHC class I cell surface receptor isoforms that resides on the...
and HLA-B
HLA-B
HLA-B is a human gene that provides instructions for making a protein that plays a critical role in the immune system. HLA-B is part of a family of genes called the human leukocyte antigen complex...
are not.
The presence of soluble HLA-G (sHLA-G) in embryos is associated with better pregnancy rate
Pregnancy rate
Pregnancy rate in infertility treatment is the success rate for pregnancy. It is the percentage of all attempts that leads to pregnancy, with attempts generally referring to menstrual cycles where insemination or any artificial equivalent is used, which may be simple artificial insemination or AI...
s. In order to optimize pregnancy rate
Pregnancy rate
Pregnancy rate in infertility treatment is the success rate for pregnancy. It is the percentage of all attempts that leads to pregnancy, with attempts generally referring to menstrual cycles where insemination or any artificial equivalent is used, which may be simple artificial insemination or AI...
s, there is significant evidence that a morphological scoring system is the best strategy for the selection of embryos. However, presence of soluble HLA-G might be considered as a second parameter if a choice has to be made between embryos of morphologically equal quality.