102 Questions
Where does hematopoiesis occur in the body?
Bone marrow
Which cells are involved in the immune system?
Lymphocytes
Which organ is considered part of the lymphoid system?
Thymus
Where does hematopoiesis begin in humans?
Embryonic yolk sac
What is the origin of all blood cells?
Hematopoietic Stem Cells (HSC)
What is the defining characteristic of stem cells?
Ability to regenerate or 'self-renew'
Which type of cell does a stem cell differentiate into early in hematopoiesis?
Lymphoid progenitor cell
What is the defining characteristic of progenitor cells during hematopoiesis?
They have lost the capacity for self-renewal
What happens to stem cells during the development of the lymphoid and myeloid lineages?
They differentiate into progenitor cells
Which cells give rise to lymphoid and myeloid progenitors?
Hematopoietic stem cells
From where do all lymphoid cells descend?
Lymphoid progenitor cells
Where do some dendritic cells come from during hematopoiesis?
Lymphoid progenitors
What is the average lifespan of a RBC (Erythrocyte)?
120 days
How long can WBCs (Leukocytes) live?
From few days to 20-30 years
What is hematopoietic homeostasis?
A continuous process maintaining a steady state in blood cell production and loss
What is one way in which steady-state regulation of hematopoiesis is accomplished?
Control of the levels and types of cytokines produced by bone-marrow stromal cells
Which cell types produce cytokines with hematopoietic activity?
Activated T cells and macrophages
What is regulated in stem cells and progenitor cells to influence hematopoiesis?
Expression of receptors for hematopoietically active cytokines
Which morphologic changes are associated with cells undergoing programmed cell death?
Decrease in cell volume, modification of the cytoskeleton, chromatin condensation, DNA degradation
Which process leads to the release of cell contents and may induce a local inflammatory response?
Necrosis
Which type of cell death does not induce a local inflammatory response?
Apoptosis
What percentage of the body’s white blood cells do lymphocytes constitute?
20%–40%
Which cells are responsible for adaptive immunity and immunologic diversity?
Lymphocytes
What is the predominant cell type in the lymph?
Lymphocytes
What is the defining characteristic of naïve lymphocytes?
They have not interacted with antigen
How are different lineages or maturational stages of lymphocytes distinguished?
By their expression of membrane molecules recognized by particular monoclonal antibodies
What are blast cells called when they interact with antigen and proliferate?
Lymphoblasts
Naïve lymphocytes have not interacted with antigen.
True
Lymphoblasts are 15μm-diameter blast cells.
True
All monoclonal antibodies that react with a particular membrane molecule are grouped together as a cluster of differentiation (CD).
True
What is the phase of the cell cycle in which resting (naive or unprimed) lymphocytes reside?
G0 phase
What do B and T lymphocytes enlarge into after antigen activation?
Lymphoblasts
At what stage can B and T lymphocytes not be distinguished morphologically?
Resting (naive or unprimed) stage
Where do B cells mature in birds?
Bursa of fabriscus
What distinguishes mature B cells from other lymphocytes?
Synthesis and display of membrane-bound immunoglobulin
What is the fate of memory B cells?
Longer life span with the same membrane-bound antibody as parent B cell
Where do T lymphocytes (T cells) mature?
Thymus
What is the main site of antigen recognition for T cells?
Cell membrane
Which subpopulation of T cells generally functions as T cytotoxic (Tc) cells?
CD8+ T cells
Which receptor do Natural Killer (NK) cells express that allows them to attach to antibodies and subsequently destroy targeted cells?
CD16
What is the primary function of Natural Killer (NK) cells in the innate immune response?
Recognize tumor or virus-infected cells
Which type of lymphocyte is large, granular, and involved in the innate immune response?
Innate lymphoid cells (ILCs)
Which cells do not express clonally distributed receptors for antigens but participate in initiating lymphocyte responses to antigens?
Mononuclear phagocytes and dendritic cells
Which cells originate in the bone marrow, circulate in the blood, and mature into macrophages in various tissues?
Monocytes
What are the cells that settle in tissues, mature, and become macrophages?
Monocytes
What is the fate of the digested antigen after phagocytosis?
Eliminated through exocytosis
What enhances phagocytosis?
Antibody attached to the antigen
What happens to some of the digested antigen after phagocytosis?
Presented on the membrane on MHC
Where are follicular dendritic cells (FDCs) primarily found?
Germinal centers of lymphoid follicles in the lymph nodes and spleen
Which type of dendritic cells has long membranous extensions resembling dendrites on nerve cells?
Langerhans DC
What is the primary role of dendritic cells in the immune system?
Induction of T lymphocyte responses to protein antigens
Which leukocyte is the first to arrive at the site of inflammation?
Neutrophils
Which leukocyte plays a role in parasitic organism defense?
Eosinophils
Which leukocyte plays a role in allergic reactions?
Basophils
Where do mature lymphocytes interact with antigens in the immune system?
Lymph nodes, spleen, and mucosa-associated lymphoid tissues
Which organs are considered primary lymphoid organs responsible for the maturation of lymphocytes?
Thymus and bone marrow
What is the function of gut-associated lymphoid tissues (GALT) in the immune system?
Trapping antigen and providing sites for mature lymphocytes to interact with that antigen
Primary organs of the immune system are thymus and bone marrow.
True
Once mature lymphocytes have been generated in the primary lymphoid organs, they circulate in the blood and lymphatic system.
True
Lymph nodes, spleen, and mucosa-associated lymphoid tissues are examples of secondary organs of the immune system.
True
Bone marrow is the site of generation of all circulating blood cells.
True
T cells mature in the thymus.
True
The function of the thymus includes generating and selecting a repertoire of T cells to protect the body from infection.
True
Where does hematopoiesis occur mostly?
Iliac bones
What is the primary function of the thymus?
Generate and select a repertoire of T cells
Where do immature B cells proliferate and differentiate?
Bone marrow
What is the primary function of the thymus?
Produce and select a repertoire of T cells to protect the body from infection
Where do T cells mature?
Thymus
What decreases with age?
Thymus function
Where is interstitial tissue fluid carried into progressively larger lymphatic vessels?
Tissue spaces
What is the fluid called after it leaves the lymph nodes?
Lymph
Where does the lymph finally drain into the circulatory system?
Thoracic duct or right lymph duct
Where are immune responses initiated?
Spleen
Which region of the lymph node contains T helper cells and dendritic cells?
Paracortex
What is the primary cell type found in the medulla of the lymph node?
Plasma cells
Where are old and defective red blood cells destroyed and removed?
Red pulp of the spleen
Which type of lymphocytes are mainly populated in the PALS (periarteriolar lymphoid sheath) of the white pulp in the spleen?
T lymphocytes
Through which vessel are blood-borne antigens and lymphocytes carried into the spleen?
Splenic artery
Where are Peyer’s patches found?
In the walls of the small intestine
Which organ defends against antigens entering through nasal and oral epithelial routes?
Tonsils
Where are the adenoids located?
In the roof of the nasopharynx
Where are M cells located?
Mucous membranes
What is the main function of Peyer's patches in the intestine?
To constitute a nodule of lymphoid follicles
Where is the antigen released after being transported across M cells?
Large basolateral pocket
Where does antigen transportation across the epithelial layer by M cells take place?
Gut-associated lymphoid tissues (GALT)
What do activated B cells differentiate into after being activated in the underlying lymphoid follicles?
IgA-producing plasma cells
What is the primary characteristic of intraepithelial lymphocytes in the outer mucosal epithelial layer?
Many are CD8 T cells expressing TCRs with limited receptor diversity for antigen
Which cells are primarily responsible for inducing a local inflammatory reaction in the skin?
Keratinocytes
What type of cells in the skin can express class II MHC molecules and function as antigen-presenting cells?
Keratinocytes
What is the main function of the epidermal layer of the skin in nonspecific (innate) defenses?
Acting as an anatomic barrier to the external environment
What is the defining characteristic of a secondary follicle?
Contains a ring of B cells surrounding germinal center
What comprises a primary follicle?
Network of follicular dendritic cells and small resting B cells
What happens to a primary follicle after antigenic activation?
It transforms into a secondary follicle
Which vertebrates lack B and T cells and cannot mount adaptive immune responses?
Jawless fishes
What do jawed vertebrates possess that jawless fishes lack?
B and T cells
What is the primary characteristic of a secondary lymphoid follicle?
Large germinal center surrounded by a dense mantle of small lymphocytes
What causes phagocytes and lymphocytes to leave the blood stream and enter the affected area during an infection?
Chemotactic signals
How do distant sites ensure activation of T cells and B cells in response to infection?
Antigen arrival at lymph nodes via lymph and dendritic cells
What brings lymphocytes and other leukocytes to the site of infection?
Inflammatory processes
Chemotactic signals are generated that can cause phagocytes and lymphocytes to leave the blood stream and enter the affected area.
True
Inflammatory processes bring only lymphocytes to the site of infection.
False
Antigen from distant sites can arrive at lymph nodes via lymph and dendritic cells, thereby assuring activation of T cells and B cells.
True
Study Notes
Hematopoiesis
- Occurs in the body mainly in the bone marrow
- Involves the development of all blood cells from hematopoietic stem cells
Immune System
- Involves lymphoid cells, including B cells and T cells, which originate from hematopoietic stem cells
- Key players: B cells, T cells, natural killer cells, dendritic cells, macrophages
Hematopoietic Stem Cells
- Define characteristic: ability to self-renew and differentiate into multiple cell types
- Early in hematopoiesis, differentiate into myeloid or lymphoid progenitor cells
- Give rise to lymphoid and myeloid progenitors, which develop into different blood cells
Progenitor Cells
- Defining characteristic: ability to differentiate into specific cell types
- During hematopoiesis, proliferate and differentiate into mature blood cells
Lymphoid and Myeloid Lineages
- Develop from hematopoietic stem cells
- Lymphoid lineage: gives rise to lymphoid cells (B cells, T cells, natural killer cells)
- Myeloid lineage: gives rise to myeloid cells (red blood cells, platelets, granulocytes, monocytes)
Blood Cells
- Red blood cells (erythrocytes): average lifespan of 120 days
- White blood cells (leukocytes): lifespan varies, some can live for years, others for only a few days
- Platelets: lifespan of 7-10 days
Lymphocytes
- Constitute 20-40% of white blood cells
- B cells: responsible for adaptive immunity and immunologic diversity
- T cells: mature in the thymus, involved in cell-mediated immunity
- Naïve lymphocytes: have not interacted with antigen, reside in G0 phase of the cell cycle
- Activated lymphocytes: enlarge and proliferate after antigen interaction
Dendritic Cells
- Originate from hematopoietic stem cells
- Primary role: antigen presentation to T cells
- Found in lymphoid organs, skin, and other tissues
Phagocytosis
- Process by which cells engulf and digest foreign particles and antigen
- Enhances phagocytosis: opsonins, complement system
- Fate of digested antigen: some is presented to T cells, some is destroyed
Immune Response
- Initiated in secondary lymphoid organs (lymph nodes, spleen, mucosa-associated lymphoid tissues)
- Involves interaction between antigen-presenting cells, T cells, and B cells
- Chemotactic signals attract phagocytes and lymphocytes to sites of infection
Lymphoid Organs
- Primary lymphoid organs: bone marrow, thymus
- Secondary lymphoid organs: lymph nodes, spleen, mucosa-associated lymphoid tissues
- Functions: maturation of lymphocytes, activation of immune responses
Test your knowledge on hematopoiesis, cells of the immune system, organs of the immune system, and evolutionary comparisons of lymphoid cells and organs. This quiz covers key concepts in immunology and hematopoiesis.
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