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HLA class II 334 HLA-DO
Human class I histocompatibility antigen (HLA-A 0201) complexed with
a decameric peptide from calreticulin HLA-A 0201. Human recombinant
extracellular fragment expressed in Escherichia coli; peptide synthesis
based on sequence of human calreticulin.
Class I histocompatibility antigen HLA-B*2705 complexed with nonapeptide
arg–arg–ile–thr–leu–lys (theoretical model).
HLA class II
Refer to MHC genes and class II MHC molecules.
HLA class II molecules
The term used to describe MHC class II molecules in humans.
HLA class III
Refer to MHC genes and class III MHC molecules.
HLA-D region
The human major histocompatibility complex (MHC) class II
region comprised of three subregions designated DR, DQ, and
DP. Multiple genetic loci are present in each of these. Each of
the DN (previously DZ) and DO subregions is comprised of
one genetic locus. Each HLA class II molecule is composed
of one α chain and one β chain that constitute a heterodimer.
Genes within each subregion encode the α and β chains of
a particular class II molecule. Class II genes that encode α
chains are designated A, and class II genes that encode β
chains are designated B. A number is used following A or B if
a particular subregion contains two or more A or B genes.
HLA disease association
Certain human leukocyte antigen (HLA) alleles occur in
higher frequencies in individuals with particular diseases
than in the general population. This type of data permits estimation
of the relative risk of developing a disease with every
known HLA allele. For example, a strong association exists
between ankylosing spondylitis, an autoimmune disorder
involving the vertebral joints, and the major histocompatibility
complex (MHC) class I allele HLA-B27. A strong association
exists between products of the polymorphic class II
alleles HLA-DR and -DQ and certain autoimmune diseases,
because MHC class II molecules are of great importance
in the selection and activation of CD4 + T lymphocytes that
regulate the immune responses against protein antigens. For
example, 95% of Caucasians with insulin-dependent (type
I) diabetes mellitus have HLA-DR3 or HLA-DR4 or both.
A strong association of HLA-DR4 with rheumatoid arthritis
also exists. Numerous other examples are the targets of current
investigations, especially in extended studies employing
DNA probes. Calculation of the relative risk (RR) and absolute
risk (AR) can be found elsewhere in this dictionary.
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HLA-DM.
MHC
Class II
HLA-DR
HLA-DM
HLA-DM
Invariant MHC class II molecule that facilitates the loading
of antigenic peptides onto major histocompatibility complex
(MHC) class II molecules in humans. As a result of proteolysis
of the invariant chain, a small fragment called the
class-II-associated invariant chain peptide (CLIP) remains
bound to the MHC class II molecule. CLIP is replaced
by antigenic peptides; however, this does not occur in the
absence of HLA-DM. The HLA-DM molecule present in
endosomal compartments plays some part in removal of
CLIP and in the loading of antigenic peptides. Although
HLA-DM is structurally similar to MHC class II molecules,
it is not polymorphic.
HLA-DO
A negative modulator of HLA-DM-mediated MHC class
II peptide loading. By stably associating with HLA-DM,
the catalytic action of HLA-DM on class II peptide loading
is inhibited. Therefore, HLA-DO affects the peptide