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MHD 493 microglobulin
Class II MHC molecules are glycoprotein histocompatibility antigens
that play a critical role in immune system cellular interactions. Each
class II MHC molecule is comprised of a 32- to 34-kDa α chain and a
29- to 32-kDa β chain, each of which possesses N-linked oligosaccharide
groups, amino termini that are extracellular, and carboxyl termini that are
intracellular. Approximately 70% of both α and β chains are extracellular.
Major histocompatibility complex (MHC) class II molecular structure.
MHD
Minimal hemolytic dose; the amount of complement used
in a complement fixation test. MHD is also an abbreviation
for minimal hemagglutinating dose of a virus, as in a
hemagglutination inhibition test.
MICA, MICB
Human MHC class I chain-related genes located within the
HLA class I region of chromosome 6 encode MHC class I
chain-related A and B. MIC proteins are markers of “stress” in
the epithelia, and act as ligands for cells expressing a common
activatory NK cell receptor (NKG2D). Heat or other environmental
stress, virus infection, or tumor regenesis may lead to
upregulation of these human stress ligands. These molecules
combine with the NK activatory receptor, NKG2D, and to
Vγ1Vδ1 T cell receptors. In mice, the corresponding Rae-1
and H60 molecules also combine with NKG2D. Refer to NK
activatory receptors and γδ T cell receptors.
MIC molecules
Major histocompatibility complex (MHC) class-I-like molecules
expressed in the gastrointestinal tract during stress.
Genes within the class I region of the human MHC encode
these molecules.
microchimerism
The establishment in a transplant recipient of passenger
donor hematopoietic cells that accompanied the solid
organ transplant.
microenvironment
An organized local interaction among cells that provides an
interactive, dynamic, structural, or functional compartmentalization.
The microenvironment may facilitate or regulate
cell and molecular interactions through biologically active
molecules. Microenvironments may exert their influence
at the organ, tissue, cellular, or molecular levels. In the
immune system, they include the thymic cortex and the
thymic medulla, which are distinct; a microenvironment of
lymphoid nodules; and a microenvironment of B cells in a
lymphoid follicle, among others.
microfilaments
Cellular organelles that comprise a network of fibers of
about 60 Å in diameter present beneath the membranes of
round cells, occupying protrusions of the cells, or extending
down microprojections such as microvilli. They are found
as highly organized and prominent bundles of filaments
concentrated in regions of surface activity during motile
processes or endocytosis. Microfilaments consist mainly
of actin, a globular 42-kDa protein. In media of appropriate
ionic strength, actin polymerizes in a double array to
form the microfilaments that are critical for cell movement,
phagocytosis, fusion of phagosomes and lysosomes, and
other important functions of cells belonging to the immune
and other systems.
microfold cells
Refer to M cells.
microglia
Non-neural brain cells derived from a macrophage-like precursor.
They are migratory and have phagocytic function.
microglial cell
Phagocytic cell in the central nervous system that is a
bone marrow-derived perivascular cell of the mononuclear
phagocyte system. In the central nervous system, it may act
as an antigen-presenting cell, functioning in a major histocompatibility
complex (MHC) class-II-restricted manner.
microglobulin
Refer to β 2 microglobulin. A globulin molecule or its
fragment with a molecular weight of 40 kDa or less.
M