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lymphocyte homing 466 lymphocyte transformation
expressed as a transmembrane- or lipid-linked cell surface
protein. The transmembrane form consists of a 188-amino
acid extracellular region, a 23-amino acid transmembrane
hydrophobic region, and a 12-amino acid intracellular
hydrophilic region ending in the C terminus. LFA-3 expression
by antigen-presenting cells that include dendritic cells,
macrophages, and B lymphocytes points to a possible role
in regulating the immune response.
lymphocyte homing
The directed migration of circulating lymphocyte subsets to
specific tissue locations. The action is regulated by adhesion
molecules (homing receptors), such as addressins, expressed
on specific tissues in different vascular beds. Selected T
cells that home specifically to intestinal lymphoid tissues
such as Peyer’s patches are directed by binding of VLA-4
integrin on their surfaces to MadCAM addressin on the
endothelia of Peyer’s patches.
lymphocyte immune globulin (injection)
Indicated for the management of allograft rejection in renal
allotransplant recipients. When administered with conventional
therapy at the time of rejection, it increases the
frequency of resolution of acute rejection episodes. May
be used also in conjunction with other immunosuppressive
therapy to delay the onset of the first rejection episode.
Indicated also for the treatment of moderate to severe
aplastic anemia patients who are unsuitable for bone marrow
transplantation. Unlabeled uses include its use as an
immunosuppressant in liver, bone marrow, heart, and other
organ transplants, treatment of multiple sclerosis, myasthenia
gravis, pure red cell aplasia, and scleroderma even
though efficacy is not fully established.
lymphocyte maturation
The development of pluripotent bone marrow precursor
cells into T or B lymphocytes that express antigen receptors
present in peripheral lymphoid tissue. B cell maturation
takes place in the bone marrow, and T cell maturation is
governed by the thymus.
lymphocyte mitogen stimulation test
An assay used for the in vitro assessment of cell-mediated
immunity in patients with immunodeficiency, autoimmunity,
infectious diseases, cancers, and chemical-induced
hypersensitivity reactions. Healthy human lymphocytes
have receptors for mitogens such as the plant lectin known
as concanavalin A (Con A), pokeweed mitogen (PWM),
Staphylococcus protein A, and chemicals. Lymphocytes
respond to these mitogens, which stimulate large numbers
of lymphocytes, without prior sensitization. In contrast
to antigens, mitogens do not require a sensitized host.
Mitogens may stimulate both B and T cells, and the
inability of lymphocytes to respond to mitogens suggests
impaired cell-mediated or humoral immunity.
lymphocyte precursors
Hematopoietic stem cell-derived immature cells in the bone
marrow or thymus that develop into lymphocytes, such as
pro-B, pre-B, pro-T, pre-T, and immature B and T cells.
lymphocyte receptor repertoire
All of the highly variable antigen receptors of B and T
lymphocytes.
lymphocyte recirculation
Lymphocyte migration through the lymphatic system from
the tissues into the blood, from which they return to the tissues
by extravasation. Refer to lymphocyte trafficking.
lymphocyte specificity
The restricted and unique epitopes a lymphocyte may be
able to bind based on its expression of only one type of
randomly generated antigen receptor gene.
lymphocyte tolerization
Inducing a lymphocyte to become anergic. In B cells, it
may follow B cell receptor engagement without T cell help
or result from receptor blockade. Tolerization of T cells may
be a consequence of lymphocyte interaction with immature
dendritic cells, modulated dendritic cells, or regulatory T
cells. Tolerization may be a consequence of insufficient
costimulation and/or intracellular suppressor signaling.
lymphocyte toxicity assay
A test to evaluate adverse reactions to drugs, especially
anticonvulsants. Incubation with liver microsomes is
believed to metabolize the drug to the in vivo metabolite
that kills lymphocytes from sensitized patients but not from
controls. Lymphocytes derived from nonreactive individuals
do not show significant lymphocyte toxicity.
lymphocyte trafficking
A process that is critical for interaction of the lymphocyte
surface antigen receptor with epitopes. Lymphocytes
continuously migrate from the blood into lymphoid and
nonlymphoid organs and back again to the blood by way
of the lymphatics and venules. Lymphocytes remain in the
blood circulation for approximately 30 minutes on each passage.
Lymphocytes in the blood circulation are exchanged
approximately 48 times per day, and about 5 × 10 11 lymphocytes
leave the circulation each day. Lymphocyte migration
is regulated during entry, transit, and exit. Because only a
few immunocompetent lymphocytes are specific for each
antigen, lymphocyte trafficking increases the probability
of interaction between the lymphocyte and the epitope for
which it is specific. Several adhesion molecules participate
in receptor–ligand interactions involved in the entry of lymphocytes
into lymphoid organs through endothelial venules.
Refer also to lymphocytes, circulating (or recirculating).
lymphocyte transfer reaction
Refer to normal lymphocyte transfer reaction.
Lymphocyte transformation.
lymphocyte transformation
An alteration in the morphology of a lymphocyte induced
by an antigen, mitogen, or virus interacting with a small,