cells and tissues of the adaptive immune system Flashcards
primary lymphoid organs
thymus and bone marrow
secondary lymphoid organs
spleen, lymph nodes, and mucosa-associated lymphoid tissue
lymphoid progenitor cells give rise to
B lymphocytes, T lymphocytes, and Natural Killer cells
CD stand for
cluster of differentiation and indicates a defined subset of cellular surface markers that identify cell type and stage of differentiation
lymphoid stem cells during prenatal period are found
in the fetal liver because bone marrow hasn’t developed yet, from here, stem cells generate precursor cells and send them into the tissues
all blood cells develop from common
CD34+ pluripotent stem cells
starting from 13th week of gestation, some stem cells migrate to the
bone marrow
in the bone marrow, stem cells produce
lymphoid progenitor cells which gives rise to B cell progenitors and T cell progenitors
B cells are generated in the
bone marrow from B cell progenitor
T cells are generated in the
thymus from T cell progenitor cells which migrate from the bone marrow into the thymus
antigen-specific receptors are localized on the surface of
T and B cells
the structure of antigen-specific receptors varies from one cell to another but they are all
identical on a single cell
naive lymphocytes
B and T cells that haven’t encountered their antigens; typically die after 1-3 months
the thymus gland is located in the mediastinum of the thoracic cavity ____ and ____ to the heart and ____ to the sternum
anterior
superior
posterior
when is the thymus at its largest and most acvtive
during the neonatal and pre-adolescent periods;
later the thymus disappears and is replaced by fat
each T cell has receptors specific for only one antigen that are generated by
gene rearrangement from multiple, inherited germline genes
T cells which are highly . reactive with self-antigens are deleted by
apoptosis
T helper cells
express CD4 and provide help for B cell growth and differentiation (T regulatory cells are a subtype of T helper cells)
cytotoxic T lymphocytes (CTLs)
express CD8 and recognize and kill virus-infected cells
functionally mature T cells then migrate
to secondary lymphoid tissues to mediate protection
T cells make contacts with
specialized epithelial cells, dendritic cells and macrophages in the thymus;
these cell-to-cell interactions provide mechanisms for the selection and differentiation of T cells useful to the immune system
cytokines produced by the stromal cell play an important role in
T cell development
generated naive T cells leave the thymus and are maintained
in the periphery without proliferating
thymoma
usually a slow-growing tumor that typically start in thymic epithelial cells; usually does not spread beyond the thymus gland
thymic carcinoma
less common but more aggressive cancer of thymic epithelial cells; generally more difficult to treat because it spreads quickly to other areas of the body
most thymomas/thymic carcinomas are diagnosed between _____ and ____ years of age when the thymus does not produce naive T cells
40
60
so they are very rare
B cells are produced in the
bone marrow during the lifespan
bone marrow
soft, sponge-like tissue in the center of most bone
bone marrow produces
white blood cells, red blood cells, and platelets
at birth all bone marrow is
red
during puberty, red marrow increasingly converts to
yellow marrow
in adult, around half of the bone marrow is ____ and half is ____
red
yellow
before birth, differentiation into B cells occurs within the ____ and then in the ____ after birth
fetal liver
bone marrow
the development of B cells involves cell-to-cell contacts with ____ and ____
stromal cells and cytoknes
many different B cells are generated, each with a unique ____ for particular antigen
specificity
B cells which react with self-antigens are
eliminated by apoptosis
lifetime production of B lymphocytes occurs
in the bone marrow
leukaemias
malignant diseases of the bone marrow and occur during hematopoietic development of either lymphoid or myeloid lineages. the overgrowth of of immature blood cells leads to a shortage of normal white blood cells (leading to increased risk of infections), red blood cells (leading to anemia), and platelets (leading to bruising)
myeloproliferative disorders
related to leukaemias in that they are characterized by the overproduction of one type of blood cell and in some cases develop into leukaemias. the most common causes of death were infection, cardiovascular disease, cerebrovascular disease, hemorrhage or thrombosis.
multiple myeloma
malignancy of plasma cells. the abnormal plasma cells produce proteins that impair the development of normal blood cells causing anemia (reduced numbers of RBCs) and leukopenia (reduced number of WBCs). infection is a major complication and a leading cause of death in patients with MM.
lymphoma
a cancer that develops in circulating blood lymphocytes after their production in the bone marrow. at the late stage, lymphomas can spread to the bone marrow. patients with lymphomas have an increased risk of infectious diseases.
lymphocytes develop from bone marrow stem cells and then mature in the primary lymphoid organs:
B cells- in the ____
T cells- in the ____
bone marrow
thymus
mature lymphocytes circulate through the blood to ____
secondary lymphoid organs (lymph nodes, spleen, and regional lymphoid tissues such as mucosa-associated lymphoid tissues)
antigens are captured from a site of infection and transported to the ____ where they are recognized by naive B and T cells and immune responses are initiated
draining lymph node
lymphocytes continuously circulate searching for their antigens in various parts of the body except
eye, brain, and testicles
in search of foreign antigens, lymphocytes enter the secondary lymphoid organs (lymph nodes) via a specialized endothelium of the postcapillary venules called
High Endothelium Venules (HEV)
cells of High Endothelium Venules (HEV) are much
higher than normal endothelial cells (bigger?) and they express high levels of adhesion molecules that serve as “homing” receptors for lymphocytes
Blood T and B lymphocytes transmigrate through HEV into the lymph nodes by mechanism of ____ and are navigated in the tissue by chemokines produced by stromal cells
diapedesis
lymphocytes may be activated by foreign antigens in lymph nodes, if not they are still
naive and return to the blood by lymphatic drainage
naive lymphocytes reenter the circulation via
efferent lymph vessels that merge into the thoracic duct
naive B cells migrate into the _____ where they look for and respond to _____
secondary lymphoid tissues
soluble foreign antigens
antigen-activated B cells proliferate and mature into
plasma cells or memory cells
plasma cells are terminally differentiated B cells which produce and secrete
large amounts of antibodies
where do antigen-activated B cells produce antibodies against microbes in the blood?
in the spleen
the spleen participates in immune responses against many types of
blood-born pathogens
t-cell zone in spleen
located centrally (also called the periarteriolar lymphoid sheath or PALS)
b-cell zone in spleen
distributed around the T zone in tightly packed follicles
plasma cells are rarely found in the peripheral blood, but they comprise from 0.2% to 2.8% of the ______ white cell count
bone marrow
in search of foreign antigens, naive T cells migrate into
secondary lymphoid organs such as lymph nodes
T cells which have been activated by antigens differentiate into
effector or memory T cells
some effector and memory T cells migrate back into the
peripheral sites of infection
some activated and differentiated T cells remain in the lymph nodes and help _____
antigen-activated B cells to become an antibody factory plasma cell
naive B and T cells enter the lymph nodes through an artery leaving the circulation by moving across the
HEV
B and T cells migrate to different zones of the lymph node directed by
chemokines that are produced in these areas by stromal cells
dendritic cells pick up antigens from the sites of antigen entry and enter through
afferent lymphatic vessels
dendritic cells migrate to the ____ areas of the lymph node
T cell-rich
in the absence of antigen stimulation, follicles are composed of small naive B cells and/or recirculating memory B cells and called
primary follicles
with antigen stimulation, B cells proliferate and differentiate converting the primary follicle into a ____ or ____
secondary follicle
germinal center
germinal centers were described more than 125 years ago as compartments that contained
mitotic B cells
antigen-presenting cells are cells that
capture, process, and display antigens to T lymphocytes and provide signals that stimulate the proliferation and differentiation of the lymphocytes
what 3 cells can serve as antigen-presenting cells
dendritic cells, macrophages, and activated B cells
only dendritic cells can activate
naive T cells in the lymph nodes
macrophages and B cells can present antigens only for
activated T cells but not naive T cells
dendritic cells and macrophages are cells of ____; thus they provide an link between
innate immunity
innate and adaptive immunity
pre-classical dendritic cells gives rise to
classical DCs
plasmacytoid DC gives rise to
plasmacytoid DCs
monocytes give rise to
inflammatory DCs
what gives rise to Langerhans cells?
fetal hemapoietic organs (yolk sac, liver) (hematopoetic stem cell –> embryonic tissue precursor –> Langerhans cells
DCs are part of ____ lineage
myeloid
DCs can be broadly divided into:
classical DCs, myeloid DCs, and plasmacytoid DCs
myeloid DCs (mDC) are derived from
monocytes
classical DCs, plasmacytoid DCs (pDC), and Langerhan’s cells in epidermis of the skin, develop directly from
stem cells
to acquire antigens, DCs use
receptor-mediated endocytosis and pinocytosis
DCs express receptors that recognize antigens typcially made by
microbes and not mammalian cells
activated DCs secrete
cytokines
classical DCs reside in
skin, mucosa, and organ parenchyma
upon activation by microbes, classical DCs migrate to
lymph nodes where they display microbial protein antigens to T lymphocytes
plasmacytoid DCs are early cellular responders to
viral infection
plasmacytoid DCs recognize
nucleic acids of intracellular viruses and produce soluble interferons (aka IFN-alpha/beta)
IFN-alpha/beta have potent
antiviral activities
