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medulla 486 membrane attack complex (MAC)
medulla
The innermost or central region of an organ. The central
area of a thymic lobe is the thymic medulla, which is rich in
antigen-presenting cells derived from the bone marrow and
medullary epithelial cells. Macrophages and plasma cells
are rich in the lymph node medulla through which lymph
passes en route to the efferent lymphatics.
medullary cord
A region of the lymph node medulla composed of macrophages
and plasma cells that lies between the lymphatic
sinusoids.
medullary sinus
Potential cavities in the lymph node medulla that receive
lymph prior to its entering efferent lymphatics.
medullary thymic epithelial cells (mTECs)
Refer to thymic epithelial cells.
Megakaryocyte.
megakaryocyte
Relatively large bone marrow giant cells of myeloid lineage
that are multinucleate and from which blood platelets are
derived by the breaking up of membrane-bound cytoplasm
to produce thrombocytes.
MEL-14
A selectin on the surfaces of lymphocytes significant in
lymphocyte interaction with endothelial cells of peripheral
lymph nodes. Selectins are important for adhesion despite
shear forces associated with circulating blood. MEL-14 is
lost from the surfaces of both granulocytes and T lymphocytes
following their activation. It combines with phosphorylated
oligosaccharides.
MEL-14 antibody
A gp90 receptor that permits lymphocyte binding to
peripheral lymph node high endothelial venules. Immature
double-negative thymocytes comprise cells that vary from
high to low in MEL-14 content. The gp90 MEL-14 epitope
is a glycoprotein on murine lymph node lymphocyte
surfaces. MEL-14 antibody prevents these lymphocytes
from binding to postcapillary venules. The gp90 MEL-14
is apparently a lymphocyte homing receptor that directs
these cells to lymph nodes in preference to lymphoid tissue
associated with the gut.
melanization reaction
Refer to ProPO system.
melanocyte
A melanin pigment-producing cell of the skin.
melanoma
Malignant tumors of melanocytes in the skin.
melanoma antigen-1 gene
See MAGE-1.
melanoma-associated antigens (MAAs)
Antigens associated with the aggressive, malignant, and
metastatic tumors arising from melanocytes or melanocyte-associated
nevus cells. Monoclonal antibodies have
identified more than 40 MAAs. They are classified as major
histocompatibility complex (MHC) molecules, cation binding
proteins, growth factor receptors, gangliosides, high
molecular weight extracellular matrix-binding molecules,
and nevomelanocyte differentiation antigens. Some of the
antigens are expressed on normal cells; others are expressed
on tumor cells. Melanoma patient blood sera often contain
anti-MAA antibodies that are regrettably not protective.
Monoclonal antibodies against MAAs aid studies on the
biology of tumor progression, immunodiagnosis, and
immunotherapy trials.
melanoma growth stimulatory activity
See MGSA.
melanosome
A melanocyte organelle linked to the endocytic pathway
that is charged with synthesis of pigment proteins.
HOOC
CH
NH 2
CH 2
CH 2 CH 2 Cl
CH 2 CH 2 Cl
Structure of melphalan (l-phenylalanine mustard).
melphalan (l-phenylalanine mustard)
Nitrogen mustard used to treat multiple myeloma patients.
Membrane perforations resulting from membrane attack complex
(MAC) action.
membrane attack complex (MAC)
Five terminal proteins (C5, C6, C7, C8, and C9) associate
into a membrane attack complex (MAC) on a target cell
membrane to mediate injury. Initiation of MAC assembly
begins with C5 cleavage into C5a and C5b fragments.
A (C5b678) 1(C9) n complex then forms either on natural
membranes or, in their absence, in combination with
such plasma inhibitors as lipoproteins, antithrombin III,
and S protein. C9 and C8 α proteins resemble each other
structurally and also in sequence homologies. Both bind
N