Cells and Organs Involves in Adaptive Immunity Flashcards
Antigen-specific B-cell receptors (BCRs)
Secrete antibody
Humoral immunity
B cells
Antigen-specific T-cell receptors (TCRs)
T-cells subsets and cytokines
Cellular immunity
T cells
_____ exhibit antigen specificity by virtue of their expression of antigen-specific T-cell receptors (TCRs).
T cells
In the case of T-cells, their participation in adaptive immune responses is as varied as the T-cell subsets and _____ they produce.
cytokines
Historically, T-cell mediated responses have been
referred to as ______
cell-mediated responses or cellular
immunity
B cells expressing antigen-specific B-cell receptors (BCRs) synthesize and secrete antibody into the bloodstream. This is often termed ______
humoral immunity
primary lymphoid organs:
bone marrow
thymus
Considered the largest tissue of the body, with a total weight of 1300 - 1500g in the adult
bone marrow
Fills the core the all long bones and is the main source of hematopoietic stem cells of the blood cell lines
bone marrow
T,B,and NK cells arise from a common precursor:
common lymphoid precursor (CLP)
The center for antigen independent lymphopoiesis
bone marrow
Site of T cells maturation
thymus
A small, flat, bilobed organ found on the thorax, weighs an average of 30 g at birth, reaches about 35 g at puberty, and then gradually atrophies
thymus
SECONDARY LYMPHOID ORGANS:
Spleen, lymph nodes, tonsils, appendix, Peyer’s patches in the intestines, and other mucosal-
associated lymphoid tissue (MALT)
Once differentiation occurs, mature T and B lymphocytes are released from the bone marrow and the thymus. They migrate to _____ and become part of a
recirculating pool.
secondary lymphoid organs
_____ where activation of lymphocytes occurs on these organs
lymphopoiesis
Largest secondary lymphoid organ, approx. 12 cm and weighing 150 g in adult
spleen
Located in the upper-left quadrant of the abdomen
spleen
A large discriminating filter, as it removes old and damaged cells and foreign antigens from the blood
spleen
makes up >1/2 of the total vol.; function is to destroy old RBCs
red pulp
approx. 20% of total wt. of spleen and contains the lymphoid tissue
white pulp
Located along lymphatic ducts and serve as central collecting points for lymph fluid from adjacent tissues
lymph nodes
primary function of lymph nodes:
Generation of B-cell memory
Accumulation of lymphocytes and other cells causes the lymph nodes to become enlarged, a condition known as ______
lymphodenopathy
The outermost layer, the _____, contains macrophages and aggregations of B cells in primary follicles similar to those found in the spleen.
cortex
These are the mature, resting B cells
that have not yet been exposed to antigen
cortex
Specialized cells called _____ are also located here. They are found only in lymphoid follicles and have long cytoplasmic processes that radiate out like tentacles. These cells exhibit a large number of receptors for antibody and complement and help to capture antigen to present to T and B cells.
follicular dendritic cells
consist of antigen-stimulated proliferating B cells.
secondary follicles
The interior of a secondary follicle is known as ______, because it is here that blast transformation of the B cells takes place
the germinal center
Plasma cells, which actively secrete
antibody, and memory cells, which are just a step away from forming plasma cells, are present. generation of _____ is a
primary function of lymph nodes.
B-cell memory
T lymphocytes are mainly localized in the ____
paracortex
T lymphocytes are in close
proximity to antigen-presenting cells called _____
interdigitating cells
The medulla is ______ but contains some T cells (in addition to B cells), macrophages, and numerous plasma cells.
less densely populated
Found in the gastrointestinal, respiratory, and urogenital tracts
Mucosal-Associated Lymphoid Tissue (MALT)
Here, macrophages and lymphocytes are localized at some of the main ports of entry for foreign organisms.
Mucosal-Associated Lymphoid Tissue (MALT)
represent a specialized type of
MALT and are located at the lower ileum of the intestinal tract
Peyer’s patches
Found in the mucous membrane lining of the oral and pharyngeal cavities
Their function is to respond to pathogens entering the respiratory and alimentary tracts
Tonsils and Appendix
An additional location of lymphoid tissue
appendix
All of these secondary organs are potential site for contact with foreign antigens which increase the probability of an immune response
Tonsils and Appendix
The epidermis contains a number of intraepidermal lymphocytes.
Most of these are T cells, which are uniquely positioned to combat any antigens that enter through the skin.
Cutaneous-Associated Lymphoid Tissue (CALT)
Proteins that appear on cell surfaces can be used as markers to differentiate T cells and B cells.
Proteins can also be used to distinguish the developmental stages of the two types of cells according to when these proteins appear
surface markers on lymphocyte
A reference in standardizing names of membrane proteins found on all human white blood cells
CLUSTERS OF DIFFERENTIATION (CD)
_____ has distinctive markers that include surface antigens CD19, CD45R, CD43, CD24, and c-Kit
Pro B-cells
Synthesis of the heavy chain part of the antibody molecule occurs
Pre B-cells
The first heavy chains synthesized are the _____, which belong to the class of immunoglobulins called ____, accompanied by an unusual light chain called a surrogate light chain
μ chains
IgM
Once the pre-B receptor (preBCR) is expressed, neighboring pre-B cells may send signals for further maturation
Pre B-cells
Distinguished by the appearance of complete IgM molecules on the cell surface
immature B cells
Completion of light chain rearrangement commits a cell to produce an antibody molecule with specificity for a particular antigen or group of related antigens. Variable regions, which occur on both the light and heavy chains, determine this specificity.
immature B-cells
Other surface proteins that appear on the immature B cell include:
CD21
CD 40
Major histocompatibility complex (MHC) class II molecules
Mature B-cells
In the spleen, immature B cells develop into mature cells known _____, which remain in the spleen in order to respond quickly to any blood-borne pathogens they may come into contact with
marginal zone B cells
Other immature B cells become _____, which are found in lymph nodes and other secondary organs
follicular B cells
Both IgM and IgD are exhibited on their surface
mature B-cells
Antigen-dependent activation of B cells takes place in the primary follicles of peripheral lymphoid tissue
Activated B-cells
Identifying markers that include CD25, which is found on both activated T and B cells and acts as
a receptor for interleukin-2 (IL-2), a growth factor produced by T cells.
Additional receptors that appear at this time are specific for other growth factors produced by T cells. When B cells are activated in this manner,
they transform into blasts that will give rise to both plasma cells and so-called memory cells.
Activated B-cells Exhibit
Spherical or ellipsoidal cells between 10 and 20 μm in size
plasma cells
plasma cells are characterized by the presence of:
Abundant cytoplasmic immunoglobulin
Little to no surface immunoglobulin
plasma cells represents the most fully differentiated lymphocyte, and its main function:
antibody production
Plasma cells are not normally found in the blood but are located in _____ in the peripheral lymphoid organs.
germinal centers
nondividing, and after several days of antibody production, they die without further proliferation
plasma cells
Also found in germinal centers and have a much longer life span than a resting B cell, represent progeny of antigen-stimulated B cells that are capable of responding to antigen with increased speed and intensity.
memory cells
They are similar in appearance to unstimulated B cells, but they remain in an activated state for months or years, ready to respond to the initial
antigen.
memory cells
_____ of circulating lymphocytes in the peripheral blood are T cells, and these become differentiated in the thymus
60-80%
Early surface markers on thymocytes (Lymphocyte precursors) that are committed to becoming T cells include ____
CD44 and CD25
Orderly rearrangement of the genes coding for the antigen receptor, distinct surface markers appear
during specific stages of development
T-cell differentiation
Maturation is an elaborate process that takes place over a _____ as cells filter through the cortex to the medulla
3-week period
Interaction with stromal cells under the influence of cytokines, especially _____, is critical for growth and differentiation
interleukin-7
Lack CD4 and CD8 markers
Rearrangement of the genes that code for the antigen receptor known as TCR begins at this stage
Rearrangement of the β chain occurs
double-negative stage
Thymocytes express both CD4 and CD8 antigens, they are called double-positive
Double positive thymocytes proliferate and then begin to rearrange the genes coding for the alpha chain
double-positive stage
Survivors of selection exhibit only one type of marker, either CD4 or CD8, and they migrate to the medulla
mature T cells
CD4+ T cells recognize antigen along with _____
MHC class II protein
while CD8+ T cells interact with
antigen and ______
MHC class I proteins
_____ bearing the CD4 receptor are termed helper, or inducer, cells, while the CD8-positive are cytotoxic T cells
T cells
These mature T cells are released from the ____ and seed peripheral lymphoid organs. Resting T cells have a life span of up to several years in these peripheral organs
thymus
Lymphocytes that do not express the markers of either T cells or B cells.
natural killer cells
plays a critical role in NK cell
development
interleukin-15
Larger than T cells and B cells at approximately 15 μm in diameter
natural killer cells
→ They contain kidney-shaped nuclei
→ Condensed chromatin and prominent
nucleoli.
→ Have a higher cytoplasmic-nuclear ratio
→ Cytoplasm contains a number of azurophilic granules.
natural killer cells
NK cells make up ____ of the circulating lymphoid pool and are found mainly in the spleen and peripheral blood
5-10%
Have the ability to mediate cytolytic reactions and kill target cells without prior exposure to them.
NK cells
They play an important role as a transitional cell bridging the innate and the acquired response to pathogens.
NK cells
The fact that they lack specificity in their response is essential to their function as early defenders against pathogens
NK cells
This gives time for the acquired response of specific T and B cells to be activated
NK cells
allows NK cells to attach to and lyse any cells that are coated with antibody
CD16
2 subsets of NK cells
A high level of CD56 and low or no CD16
Some CD56 and high levels of CD16
produce more cytokines and help support antibody production
A high level of CD56 and low or no CD16
have a higher cytotoxic activity
Some CD56 and high levels of CD16
NK cell activity is stimulated by exposure to cytokines such as:
Interleukin-12
Interferon gamma
Interferon beta
Since these rises rapidly during a viral infection, NK cells are able to respond early on during an infection, and their activity peaks in about 3 days, well before antibody production or a cytotoxic T cell response
NK cells
