Basic Components of the Immune System

Question 1

The process by which hematopoietic stem cells (HSCs) differentiate into mature blood cells is called

Answer 1

Hematopoiesis

Question 2

Primary lymphoid organs

Answer 2

Bone marrow and the Thymus

regulate the development of immune cells from immature precursors

Question 3

Secondary lymphoid organs:

Answer 3

•Including the spleen, lymph nodes, and specialized sites in the gut and other mucosal tissues

–Coordinate the encounter of antigen with antigen-specific lymphocytes and their development into effector and memory cells.

Question 4

HSCs are defined by two capacities:

Answer 4

1. The ability to regenerate or “self-renew”
2. The ability to differentiate into all diverse blood cell types.

Question 5

One HSC is present per ________ cells in the bone marrow.

Answer 5

5 x 10⁴ (rare)

Question 6

Myeloid cells and NK cells:

Answer 6

Are memembers of the innate immune system

First cells to respond to infection or other insults

Question 7

Lymphocytes are:

Answer 7

Members of the adaptive immune response

Generate a refined antigen specific immune response that also gives rise to immune memory

Question 8

Granulocytes:

Answer 8

Neutrophils, Basophils, Mast cells, and Eosinophils

• All granulocytes have multilobed nuclei
• The cytoplasm contains granules that are released in response to contact with pathogens

Question 9

Monocytes:

Answer 9

• Migrate into tissues in response to infection
• Can differentiate into specific tissue macrophages:
  
  • Osteoclasts in the bone
  • Microglial cells in the central nervous system
  • Alveolar macrophages in the lung

Question 10

Myeloid Antigen-Presenting Cells:

Answer 10

• Monocytes, macrophages, and dendritic cells
• Professional antigen-presenting cell (APC)
• Considered cellular bridges between the innate and adaptive immune systems

Question 12

Cells of the Lymphoid Lineage Regulate:

Answer 12

Adaptive Immune Response

Question 13

Lymphocytes:

Three major populations:

Answer 13

– Principal cell players in the adaptive immune response.

– 20% to 40% of circulating white blood cells and 99% of cells in the lymph.

1. B lymphocytes (B cells), expresses B cell Receptor
2. T lymphocytes (T cells), expresses T cell Receptor
   
   1. No contact With antigen: naïve
   2. Contact antigen: lymphocytes proliferate and differentiate into both effector cells and memory cells.
3. Natural Killer Cells (NK cells)

Question 14

B Lymphocyte (B cell): Derived its letter from its site of maturation

Bursa of Fabricius in birds

Bone marrow in mammals

Mature B cells Display ___________

Answer 14

• Display B-cell receptor (BCR)
  
  • Membrane-bound immunoglobulin (antibody) molecule that binds to antigen.
  • Can recognize soluble or particulate antigen
• – Activated B cells differentiate into effector cells known as Plasma cells
  
  • lose expression of BCR and become highly specialized for secretion of antibody

Question 15

T Lymphocytes:

Derive their letter (T) from their site of maturation in the thymus

Expresses a unique antigen-binding receptor called the

Answer 15

T-cell receptor

–Only recognize processed pieces of antigen (typically peptides) bound to cell membrane proteins called major histocompatibility complex (MHC)

Question 16

T lymphocytes are divided into two major cell types:

Answer 16

1. T cytotoxic (TC), expresses CD8
2. T helper (TH) cells, Expresses CD4
   
   1. T helper type 1 (TH1) cells regulate the immune response to intracellular pathogens
   2. T helper type 2 (TH2) cells regulate the response to many extracellular pathogens.
   3. T helper type 17 cells (TH17), so named because they secrete IL-17, play an important role in cell-mediated immunity and may help the defense against fungi.

Question 17

NK Cells

Answer 17

Natural Killer Cells

• They are lymphoid cells that are closely related to B and T cells.
• They do not express antigen specific receptors and are considered part of the innate immune system
• They distinguish cells that should be killed from normal cells. How? By “recognizing” the absence of MHC class I, which is expressed by almost all normal cells.
• Express receptors for immunoglobulins, allows them to bind antibodies specific for pathogens .
  
  • This allows NK cell to releases its granules and induces cell death.

Question 18

Provides niches for hematopoietic stem cells to self-renew and differentiate into myeloid cells and B lymphocytes

Answer 18

Bone Marrow

Question 19

Most active sites of hematopoiesis

Answer 19

• Long bones (femur, humerus)
• Hip bones (ileum)
• Sternum

Question 20

Bone marrow contains several cell types that coordinate HSC development:

Answer 20

• Osteoblasts that generate bone and control the differentiation of HSCs
• Endothelial cells that line the blood vessels and also regulate HSC differentiation
• Reticular cells that send processes connecting cells to bone and blood vessels
• Sympathetic neurons , which can control the release of hematopoietic cells from the bone marrow.

Question 21

Primary lymphoid organ located above the heart where T cells mature

Answer 21

Thymus

Question 22

Microenvironments of the thymus

Answer 22

• Cortex which is densely populated with immature thymocytes
• Medulla, which is sparsely populated with mature thymocytes.
• These major regions are separated by the corticomedullary junction (CMJ) : Cells enter from and exit to the bloodstream.

Question 23

_________ are positively selected in the cortex

__________ are negatively selected in the medulla

Answer 23

Thymocytes

Autoreactive thymocytes

Question 24

Where the immune response is initiated

Answer 24

Secondary Lymphoid Organs

Question 25

Secondary Lymphoid Organs are distributed throughout the body and share some anatomical features

Answer 25

1. Lymph nodes
2. Spleen
   
   1. Both are the most highly organized of the secondary lymphoid organs and are compartmentalized from the rest of the body by a fibrous capsule
3. Mucosa-associated lymphoid tissue (MALT)
   
   1. less organized system
   2. Found associated with the linings of multiple organ systems, including the gastrointestinal (GI) and respiratory tracts
      
      1. Tonsils
      2. Peyer’s patches (in the small intestine)
      3. Appendix
      4. Lymphoid follicles within the lamina propria of the intestines and in the mucous membranes lining the upper airways, bronchi, and genitourinary tract.

Question 26

SLOs share key features:

Answer 26

1. All have anatomically distinct regions of T-cell and B-cell activity.
2. All develop lymphoid follicles:
   
   1. highly organized microenvironments that are responsible for the development and selection of B cells that produce high affinity antibodies.

Question 27

Lymphoid Organs Are Connected to:

Answer 27

Each other and to infected tissue

–Connected by two different circulatory systems: Blood and Lymphatics

Question 28

Blood has access to:

Answer 28

virtually every organ and tissue and is lined by endothelial cells that are very responsive to inflammatory signals

Question 29

The lymphatic system is:

Answer 29

a network of thin walled vessels that play a major role in immune cell trafficking, including:

• The travel of antigen and antigen-presenting cells to SLO’s
• Used for exit of lymphocytes from lymph nodes.
• Lymph vessels are filled with a protein-rich fluid (lymph)
  
  • Lymph is derived from the fluid component of blood (plasma)
  • 2.9 liters seeps daily.

Question 30

Mechanism of lymphatic system

Answer 30

• Foreign antigen gains entrance→ picked up by the lymphatic system→ carried to Lymph nodes that traps the antigen
• Lymph becomes enriched in specific leukocytes, including lymphocytes, dendritic cells, and macrophages.

Question 31

Where are most secondary lymphoid tissues situated?

Answer 31

•Most secondary lymphoid tissues are situated along the vessels of the lymphatic system.

–The spleen is an exception and is served only by blood vessels.

Question 32

All immune cells that traffic through tissues, blood, and lymph nodes are guided by small molecules known as _______

Answer 32

chemokines

Proteins are secreted by stromal cells, antigen presenting cells, lymphocytes, and granulocytes, and form gradients that act as attractants and guides for other immune cells

Question 33

SLO: Lymph nodes

They are:

Answer 33

• Encapsulated
• Bean-shaped structures that include:
  
  • Stromal cells packed with lymphocytes, macrophages, and dendritic cells.
• Connected to both blood vessels and lymphatic vessels
• Lymph nodes are the first organized lymphoid structure to encounter antigens that enter the tissue spaces.
• Provides ideal microenvironments for encounters between antigen and lymphocytes
  
  • Results in productive, organized cellular and humoral immune responses.

Question 34

Features of the lymph node structure:

Answer 34

• Cortex contains lymphocytes (mostly B cells), macrophages, and follicular dendritic cells arranged in follicles.
• Paracortex which is populated largely by T lymphocytes and also contains dendritic cells that migrated from tissues to the node.
• Medulla is the innermost layer, and the site where lymphocytes exit the lymph node through the outgoing (efferent) lymphatics
• Germinal centers are substructures that facilitate the generation of B cells with increased receptor affinities.

Question 35

Spleen

Answer 35

• Organizes the Immune Response Against Blood-Borne Pathogens
• Situated high in the left side of the abdominal cavity
• Filtering blood and trapping blood-borne antigens
• Important in the response to systemic infections.