Untitled - D Ank Unlimited

lck, fyn, ZAP (phosphotyrosine kinases in T cells) 443 lectin
lck, fyn, ZAP (phosphotyrosine kinases in T cells)
The phosphotyrosine kinases (PTKs) associated with early
signal transduction in T cell activation. Lck is a src-type
PTK found on T cells in physical association with CD4
and CD8 cytoplasmic regions. Deficiency of lck results
in decreased stimulation of T cells and decreased T cell
growth. Fyn is also a src PTK; it is found on hematopoietic
cells. Increased fyn results in enhanced T cell activation,
but a deficiency of fyn has not been shown to decrease
T cell growth. A fyn deficiency inhibits T cell activation
in only some T cell subsets. ZAP, or ζ-associated protein
kinase, is like the syk PTK in B cells. It is found only on T
cells and natural killer (NK) cells. Activity of the enzyme is
dependent on association of ZAP with the ζ chain following
T cell receptor (TCR) activation.
LCM
Refer to lymphocytic choriomeningitis.
LD 50
The dose of a substance, such as a bacterial toxin or microbial
suspension, that leads to the death of 50% of a group of
test animals within a certain period following administration.
The measurement is employed to evaluate toxicity or
virulence and the protective qualities of vaccines administered
to experimental animals.
LDCF (lymphocyte-derived chemotactic factor)
Lymphokines that are chemotactic factors, especially for
mononuclear phagocytes.
LE factor
Hematoxylin
body
Lymphocyte
Swelling
Dissolution
C
C
Complement
Formation of a lupus erythematosus (LE) cell.
Lupus erythematosus (LE) cell.
C
LE cell
Phagocytosis
PMN
LE cell
A neutrophil (polymorphonuclear neutrophil, or PMN) in
the peripheral blood or synovia of lupus erythematosus
(LE) patients produced when the PMNs phagocytize with
Wright’s stain, a reddish-purple staining homogeneous
lymphocyte nucleus coated with antinuclear antibody. In
addition to LE, these cells are seen also in scleroderma,
drug-induced lupus erythematosus, and lupoid hepatitis.
LE cell “prep”
Glass beads are added to heparinized blood samples, causing
the release of nuclei from some blood cells that become
coated with antinuclear antibody present in the serum.
These opsonized nuclei are then phagocytized by polymorphonuclear
neutrophils to produce lupus erythematosus
(LE) cells. The LE cells produce homogeneous chromatin
that imparts a glassy appearance to the phagocytized
nuclear material.
LE cell test
A no-longer-used diagnostic test that detects antinuclear
antibodies in the sera of systemic lupus erythematosus
(SLE) patients. Antinuclear antibodies in the serum react
with nascent lymphocyte nuclei and serve as opsonins,
enhancing phagocytosis of the nucleus–antibody complex
by polymorphonuclear neutrophils. Thus, the so-called
LE cell is represented by the appearance of a polymorphonuclear
neutrophil with its own nucleus displaced to the
periphery by an ingested lymphocyte nucleus that appears
as a homogeneous mass and is coated with antinuclear
antibody. These cells develop following incubation of blood
containing the appropriate antibody for 1 hour at 37°C.
This early diagnostic test for the presence of antinuclear
antibody in SLE has been replaced by a more sophisticated
test. LE cells are also present in other connective tissue
diseases in addition to SLE.
LE factor
Antinuclear antibodies present in the blood sera of systemic
lupus erythematosus patients. LE factor facilitates
LE cell formation.
leader peptide
A 20-amino acid sequence situated at the N termini of free
heavy and light polypeptide chains and absent in secreted
immunoglobulins. Once the light and heavy polypeptide
chains reach the cisternal space of the endoplasmic reticulum,
the peptide is split from the polypeptide chains. It is thought
to facilitate vectorial release of the chains and their secretions.
leader sequence
Refer to leader peptide.
leading front technique
A method to assay chemotaxis or cell migration that
evaluates differences in the migration of stimulated and
nonstimulated cells.
lectin
A glycoprotein that binds to specific sugars and oligosaccharides
and links to glycoproteins or glycolipids on cell
surfaces. They can be extracted from plants, seeds, and
other sources. They are able to agglutinate cells such as
erythrocytes through recognition of specific oligosaccharides
and occasionally react with a specific monosaccharide.
Many lectins also function as mitogens and induce
lymphocyte transformation, during which a small resting
lymphocyte becomes a large blast cell that may undergo
mitosis. Well known mitogens used in experimental
L