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lymphocyte-activating factor (LAF) 464 lymphocyte antigen receptor complex
Small lymphocyte in peripheral blood.
Lymphocytes in peripheral blood.
Lymphocyte (scanning electron microscope).
addition, natural killer cells, which are large granular lymphocytes,
comprise a small percentage of the lymphocyte
population. Lymphocytes express variable cell surface
receptors for antigen.
lymphocyte-activating factor (LAF)
Refer to interleukin-1.
lymphocyte activation
The stimulation of lymphocytes in vitro by an antigen or
mitogen that renders them metabolically active. Activated
lymphocytes may undergo transformation or blastogenesis.
Follows binding of numerous copies of a specific
epitope to a resting lymphocyte’s TCR or BCR, resulting
in formation of a lymphoblast that undergoes proliferation.
Costimulation and cytokines are also necessary to activate
naïve cells. There is triggering of multiple genes leading the
progeny cells to undergo alterations that result in memory
and effector lymphocytes.
Stimulus
S
G 1
Blast
24
hrs.
G 2
Resting lymphocyte
M
Cell division
Lymphocyte activation.
Effector cells
Memory cell
lymphocyte activation threshold
The number of receptors for antigen required to be aggregated
and activated, together with costimulatory signals, to
produce a proliferative signal.
lymphocyte anergy
The failure of clones of T or B lymphocytes to react to
antigen; may represent a mechanism to maintain immunologic
tolerance to self. Antigen stimulation of a lymphocyte
without costimulation leads to tolerance. Unresponsiveness
may stem from a failure of T lymphocytes to proliferate on
rechallenge with antigen presented by professional antigenpresenting
cells. Occupancy of the T cell receptor by
peptide–MHC complexes leads to anergy. IL2 and selected
other cytokines are inhibited in anergic T cell clones.
Anergy appears to be a growth arrest condition designed to
diminish proliferation in the T cell immune response. Also
called clonal anergy.
lymphocyte antigen receptor complex
Immunoglobulin α (Igα) and Igβ function in B lymphocytes
as CD3 and proteins do in T cells. Requisite for signal
transduction are immunoreceptor tyrosine-based activation
motifs (ITAMs) in the cytoplasmic domains of Igα and Igβ.
Cross linking of the B cell receptor complex by antigen
leads to increased cell size and cytoplasmic ribonucleic acid
with increased biosynthetic organelles including ribosomes
as resting cells enter the G 1 stage in the cell cycle.
Class II molecules and B7-2 and B7-1 costimulators show
increased expression. B cells stimulated by antigen are then
able to activate helper T cells. Expression of receptors for
T cell cytokines increases, thereby facilitating the ability
of antigen-specific B cells to receive T cell help. The
effect of B cell receptor complex signaling on proliferation
and differentiation depends in part on the type of antigen.
Following activation as a result of combination with antigen,
cell proliferation and differentiation are facilitated by
interaction with helper T lymphocytes. Helper T cells must
recognize antigen, and there must be interaction between
protein antigen-specific B cells and T lymphocytes for
antibody to be formed. When B cells, acting as antigenpresenting
cells, interact with helper T lymphocytes that are
specific for the peptide presented, numerous ligand-receptor
interactions facilitate transmission of signals to B cells
required to generate a humoral immune response. Among
these are B7 molecules:CD28 and CD40:CD40 ligand