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methyl green pyronin stain 491 MHC class II transactivator (CIITA)
megaloblastic anemia. It interferes with the binding of IL1β
to its receptor and may function as an anticytokine.
methyl green pyronin stain
A stain used in histology or histopathology that renders
DNA green and RNA red. It is widely used to demonstrate
plasma cells and lymphoblasts that contain multiple ribosomes
containing RNA in their cytoplasm.
metronidazole
The drug of choice to treat intestinal and extraintestinal
amebiasis and neurogenital trichomoniasis and an alternative
drug for the treatment of Giardia lamblia, Balantidium
coli, and Blastocystis hominis infections.
MGSA (melanoma growth-stimulating activity)
MGSA is a chemokine of the α (CXC) family. It is a mitogenic
polypeptide secreted by human melanoma cells. The
MGSA/GRO-α gene product has powerful chemotactic,
growth regulatory, and transforming functions. Its many
tissue sources include monocytes, neutrophils, bronchoalveolar
macrophages, and endothelial cells, among other cell
types. Neutrophils, lymphocytes, monocytes, and epidermal
melanocytes are target cells.
MGUS
Refer to monoclonal gammopathy of undetermined
significance.
MHC
Abbreviation for major histocompatibility complex.
MHC-I antigen presentation
Proteins in the cytosol, such as those derived from
viruses, may be processed through the class I MHC route
of antigen presentation. The multiprotein complex in the
cytoplasm known as the proteasome effect involves proteolytic
degradation of proteins in the cytoplasm to yield
many of the peptides presented by class I MHC molecules.
TAP molecules transport peptides from the cytoplasm to
the endoplasmic reticulum where they interact with and
bind to class I MHC dimeric molecules. Once the class I
MHC molecules have become stabilized through peptide
binding, the complex leaves the endoplasmic reticulum,
entering the Golgi apparatus en route to cell surfaces.
Thus, mechanisms are provided through MHC-restricted
antigen presentation to guarantee that peptides derived
from extracellular microbial proteins can be presented
by class II MHC molecules to CD4 + helper T cells and
that peptides derived from intracellular microbes can be
presented by class I MHC molecules to CD8 + cytotoxic
T lymphocytes. The generation of microbial peptides
produced through antigen processing to combine with
self MHC molecules is critical to the development of an
appropriate immune response.
MHC class I deficiency
A type of severe combined immunodeficiency in which MHC
class I molecules are not expressed on lymphocyte membranes.
The trait has an autosomal-recessive mode of inheritance.
MHC class I molecules
Major histocompatibility complex polymorphic glycoproteins
that present cytosol-generated peptides to CD8 + T
lymphocytes. They are heterodimers comprised of a class I
heavy chain associated with β 2 microglobulin.
MHC class IB molecules
Molecules encoded by the major histocompatibility complex
that are less polymorphic than the MHC class I and class II
molecules and which present a restricted set of antigens.
MHC class Ib and IIb
MHC proteins that are nonclassical and have restricted
polymorphism. The majority do not participate in antigen
presentation. Genes at the Q, T, and M loci in mice and
genes at the HLA-X, -E, -J, -G and -F and HFE loci in
humans encode class Ib proteins. Murine P locus genes
and human DM and DO loci genes encode class IIb
proteins.
MHC class I proteins
Heterodimeric proteins on cell surfaces comprised of a
polymorphic transmembrane MHC class Iα chain noncovalently
united with an invariant β 2 microglobulin (β 2m) chain.
Murine genes in the K and D loci and human genes in the
HLA-A, -B, and -C loci encode the MHC class I α chain,
whereas the β 2m is encoded independent of the MHC. These
molecules unite with 8 to 10 endogenous amino acid peptides
that they present to CD4 + T cells. Nearly all nucleated
cells of the body express them.
MHC class II molecules
Major histocompatibility complex molecules that present
peptides formed in intracellular vesicles to CD4 + T cells.
Structurally they are heterodimers of class IIα and class
IIβ chains.
MHC class II compartment (MIIC)
A cellular site where MHC class II molecules concentrate,
interact with HLA-DM, and bind antigenic peptides prior to
migrating to the cell surface.
MHC class II deficiency
A type of combined immunodeficiency in which lymphocytes
and monocytes fail to express MHC class II molecules
on their surfaces. The cells also have diminished expression
of MHC class I antigens. The condition, which appears
principally in North African children, has an autosomalrecessive
mode of inheritance. Patients are able to synthesize
the class I invariant chain β 2 microglobulin. Whereas
the numbers of B cells and T lymphocytes in the circulating
blood are normal, patients have agammaglobulinemia and
diminished cell-mediated immunity. Malabsorption in the
gastrointestinal tract and diarrhea are commonly associated
with this deficiency.
MHC class II proteins
Heterodimeric proteins on cell surfaces comprised of polymorphic
MHC class IIα and class IIβ chains. Genes at the
A and E murine loci and by DP, DQ, and DR loci genes in
humans encode the α and β chains. These proteins unite with
13 to 18 exogenous amino acid peptides that are then presented
to CD4 + T cells. Antigen-presenting cells express them.
MHC class II region
Region composed of three subregions designated DR, DQ,
and DP. Multiple genetic loci are present in each subregion.
DN (previously DZ) and DO subregions are composed of a
single genetic locus. Each class II HLA molecule includes
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; 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.
MHC class II transactivator (CIITA)
A protein that activates major histocompatibility complex
(MHC) class II gene transcription. The gene that encodes
this molecule is one of several defective genes in bare
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