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maturation of affinity 483 Mcg isotypic determinant
remodeling of connective tissues. The gelatinase-type
MMPs synthesized by T lymphocytes mainly facilitate T
cell migration. MMPs facilitate shedding of L-selectin, an
adhesion receptor, from the leukocyte surface.
maturation of affinity
During the course of immunization with a particular antigen,
the antibodies formed show a progressive increase in affinity.
mature B cells
B lymphocytes that expresses immunoglobulin M (IgM) and
IgD and are functionally capable of responding to antigen.
These cells constitute the final step in B cell maturation of
the bone marrow and reside in peripheral lymphoid organs.
mature dendritic cells
Antigen-presenting cells of secondary lymphoid tissues
that bear costimulatory molecules among other cell surface
molecules that render them capable of presenting antigen to
naïve T cells that become activated.
mature T cells
Classified on the basis of their surface markers, such as
CD4 and CD8. CD4 + T lymphocytes recognize antigens in
the context of MHC class II histocompatibility molecules,
whereas CD8 + T lymphocytes recognize antigen in the
context of MHC class I molecules. CD4 + T cells participate
in the afferent limb of the immune response to exogenous
antigen via antigen-presenting cells. This stimulates the
synthesis of interleukin-2 (IL2), which activates CD8 +
T cells, natural killer (NK) cells, and B cells, thereby
orchestrating an immune response to the antigen. Thus
these cells are called helper T lymphocytes. They also
mediate delayed-type hypersensitivity reactions. CD8 + T
lymphocytes include cytotoxic and suppressor cell populations.
They react to endogenous antigen and often express
their effector function through a cytotoxic mechanism (e.g.,
against a virus-infected cell). Other molecules on mature
T cells in humans include the E rosette receptor CD2 molecule,
the T cell receptor, the pan T cell marker (CD3), and
transferrin receptor.
Matzinger danger theory
A concept that abandons the idea of self–nonself discrimination
as the basic immunologic metaphor. Matzinger
proposes that the function of the immune system is to
protect the individual from “danger.” His concept requires
a discriminating event to mark the entry of potentially
dangerous material into the system. This is associated with
the activity of antigen-presenting cells, which at rest are
unable to provide a source of signal 2, which expresses the
S phenotype. A dangerous event converts this cell to the S +
state that provides costimulatory activity, signal 2 for the
initiation of the T cell response, and subsequent T-celldependent
immune phenomena.
Mayer, Manfred
A student of Michael Heidelberger and later a professor at
Johns Hopkins University Medical School in Baltimore,
Mayer was an authority on the molecular aspects of complement
activity, especially its role in hemolysis.
MBP
Acronym for (1) myelin basic protein or (2) major basic protein.
MBSA
Acronym for methylated bovine serum albumin.
McCleod phenotype
Human erythrocytes without Kell or Cellano antigens.
These red cells lack Kx, a precursor in the biosynthetic
Manfred M. Mayer.
pathway of the Kell blood group system. Kx is encoded by
a gene on the X chromosome termed X1k and is normally
found on granulocytes and fibroblasts. Red cells lacking Kx
exhibit decreased survival and diminished permeability to
water and are acanthocytic morphologically with spikes on
their surfaces. They also show decreased expression of Kell
system antigens. This group of erythrocyte abnormalities
is termed the McCleod phenotype. Subjects with McCleod
erythrocytes have a neuromuscular system abnormality
characterized by elevated serum levels of creatine phosphokinase
(CPK). Older individuals may have disordered
muscular functions. The X1k gene maps to the short arm of
the X chromosome, where it is linked to the chronic granulomatous
disease gene.
M cell
A gastrointestinal tract epithelial cell, with an intraepithelial
pocket that trayscytoses antigens from a lumen
such as the gastrointestinal tract across the epithelium to
its basolateral surface. The M cell conveys microorganisms
and macromolecular substances from the gut lumen
to Peyer’s patches. M cells do not possess glycocalyx and
brush borders that enable antigen capture. M cells are
non-antigen-presenting cells found in the epithelial layers
of Peyer’s patches that nevertheless may have an important
role in antigen delivery. They have relatively large surfaces
with microfolds that attach to microorganisms and macromolecular
surfaces. The M cell cytoplasmic processes
extend to CD4 + T cells underneath them. Materials attached
to microvilli are conveyed to coated pits and moved to the
basolateral surface, which has pronounced invaginations
rich in leukocytes and mononuclear phagocytes. Thus,
materials gaining access by way of M cells come into
contact with lymphoid cells as they reach the basolateral
surface. This is believed to facilitate induction of immune
responsiveness. M signifies membranous or microfold cells.
Mcg isotypic determinant
A human immunoglobulin λ chain epitope that occurs on
a number of every person’s λ light polypeptide chains in
immunoglobulin molecules. The Mcg isotypic determinant
is characterized by asparagine at position 112, threonine at
position 114, and lysine at position 163.
M