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lectin-like receptors 444 lepra cells
immunology include phytohemagglutinin, pokeweed mitogen,
and concanavalin A.
lectin-like receptors
Macrophage and monocyte surface structures that bind
sugar residues. The ability of these receptors to anchor
polysaccharides and glycoproteins facilitates attachment
during phagocytosis of microorganisms. Steroid hormones
elevate the number of these cell surface receptors.
lectin pathway of complement activation
A complement-activation pathway, not involving antibody,
that is initiated by the binding of microbial polysaccharide
to circulating lectins such as the plasma mannose-binding
lectin (MBL) which structurally resembles C1q. Similar to
C1q, it activates the C1r–C1s enzyme complex or another
serine esterase, termed mannose-binding protein-associated
serine esterase. Involves MASP1/2, MAp19 and C4, C2,
and C3 cleavage and activation. Beginning with C4 cleavage,
the lectin pathway is the same as the classical pathway.
Lederberg, Joshua (1925–2008)
American biochemist who made a significant contribution
to immunology with his work on the clonal selection theory
of antibody formation. He received a Nobel Prize in 1958
(with Beadle and Tatum) for his research on genetic recombination
and organization of genetic material in bacteria.
LEF-1
Lymphoid enhancer factor 1 (LEF-1) is a cell-type-specific
transcription factor and member of the family of high
motility group (HMG) domain proteins that recognizes a
specific nucleotide sequence in the T cell receptor (TCR)
α enhancer. The function of LEF-1 is dependent, in part,
on the HMG domain, which induces a sharp bend in the
DNA helix, and on an activation domain, which stimulates
transcription only in the specific context of other enhancerbinding
proteins.
leflunomide
A prodrug of an inhibitor of pyrimidine synthesis. An isoxazole
immunomodulatory agent that blocks dihydroorotate
dehydrogenase, an enzyme involved in de novo pyrimidine
synthesis that has antiproliferative effects. Leflunomide has
an anti-inflammatory effect. Its active metabolite has a long
half-life of several weeks. It is approved only for treatment
of rheumatoid arthritis but may have future potential in
combination with mycophenolate mofetil in the treatment
of selected autoimmune and inflammatory skin disorders,
as well as in combating allograft rejection for solid organ
transplants. Toxicities include some risk of liver injury,
renal impairment and teratogenic effects.
Legionella immunity
Immunity against Legionella pneumophila, a facultative
intracellular pathogen that induces Legionnaires’ disease in
humans, depends on cellular immune mechanisms, including
the release of IFN-γ. T H1 CD4 + T cells play a significant
role in the development of acquired immunity in mice.
Acquired immunity to Legionella pneumophila is believed
to be a consequence of both humoral and cellular immune
responses that facilitate enhanced uptake of the microorganisms
by activated mononuclear phagocytic cells.
Leishmania
An obligate intracellular protozoan parasite with an affinity
for infecting macrophages. It produces chronic inflammatory
disease of numerous tissues. In mice, Th1 responses
to Leishmania major, including IFN-γ-synthesis, control
infection. By contrast, Th2 responses to IL4 synthesis result
in disseminated lethal disease.
leishmaniasis
A parasitic human infection that can lead to the development
of various disease conditions ranging from cutaneous
lesions to fatal visceral infection. Mouse models of
infection have yielded much information on mechanisms
of susceptibility and resistance to this infection, rendering
experimental leishmaniasis. This is a fine model system to
evaluate T cell subset polarization and its relationship to
pathogenesis. These intracellular protozoan parasites affect
12 million people worldwide. Leishmania major and L.
tropica may cause cutaneous leishmaniasis; L. baraziliensas
causes mucocutaneous leishmaniasis; and L. donovini
and L. infantum induce visceral leishmaniasis to produce
the clinical disease known as kala-azar (black disease),
dum dum fever, or ponos. This disease follows the spread
of the parasite from a skin lesion to tissue macrophages in
the liver, spleen, and bone marrow. Patients develop fever,
malaise, weight loss, coughing, and diarrhea, anemia, darkening
skin, and hepatosplenomegaly. Immunity depends
on polarization of CD4 + Th cell subsets. In a Th2 response
to infection, interleukin-4 (IL4) and IL10 correlate with
disease susceptibility, whereas a murine Th1 response is
associated with production of interferon γ (IFN-γ) and IL2,
which lead to resolution of lesions in animals that remain
refractory to further challenge.
lenalidomide (oral)
An immunomodulatory and antiangiogenic agent, whose
mechanism of action remains to be fully determined. It
blocks the secretion of proinflammatory cytokines and
increases the secretion of anti-inflammatory cytokines from
peripheral blood mononuclear cells. It inhibits the expression
of cyclooxygenase-2 (COX-2) but not COX-1 in vitro.
lens-induced uveitis
An inflammatory reaction in the eye related to sensitization
or toxicity to lens material. It also includes inflammation
that occurs following dislocation and breakdown of the lens.
The lens contains very strong organ-specific antigen that
can stimulate the formation of autoantibodies. Lens antigens
are normally sequestered and do not induce antibody
responses until exposed to the immune system of the host.
The principal lens antigen is α crystallin. Evidence that
lens-induced uveitis is an immunological disease is based
mainly on animal studies, in which its potent immunogenic
properties and capacity to produce autoimmune disease
have been revealed. The condition is treated by surgically
removing the lens or its remnants soon after diagnosis.
lentiviruses
A group of slow retroviruses that have long incubation periods
and take years to manifest. Human immunodeficiency
virus (HIV) is included in this group.
LEP (low egg passage)
A type of vaccine for rabies that has been employed for the
immunization of dogs and cats.
Lepow, Irwin
Lepow and Louis Pillemer were instrumental in describing
the alternative pathway of complement activation.
lepra cells
Foamy macrophages that contain clusters of
Mycobacterium leprae microorganisms that are not
degraded because cell-mediated immunity has been lost.