MOD 1: Intro to Immune System

Question 1

2 Branches of Immune System

Answer 1

-Innate immune system
-Adaptive immune system

Question 2

Functions of Immune System (2)

Answer 2

Discriminate- Recognize self from non-self

Eliminate- Destroy non-self (e.g. pathogen) and altered self-cells (e.g. cancer)

Question 3

Dysfunctions of the Immune System (2)

Answer 3

Autoimmunity and Hypersensitivity- Misdirected or overly active immune system

Immunodeficiency- Underactive immune system (e.g. acquired immunodeficiency syndrome - AIDS)

Question 4

Antigen

Answer 4

foreign protein that induces an immune response, typically including the production of antibodies. Antigen is a contraction of the words “antibody generator”.

Question 5

Antibody

Answer 5

protein that is produced in response to, and countering, a specific antigen.

Question 6

Relationship b/t antigen and antibody

Answer 6

Antibodies bind to foreign substances (antigens) in the body and provide a signal for their elimination.

Question 7

What do you think is most important for defence mechanisms to work properly

Answer 7

BALANCE

Each component and process needs to be functional, otherwise you will experience a defect that leads to immunodeficiencies. But it also needs to be controlled and regulated, otherwise you risk an overstimulated immune system that is not able to perform the subtle actions needed to attack foreign molecules while preserving the authenticity of the body’s structures. If the balance shifts in this opposite direction, this can lead to autoimmune disorders

Question 8

Lymphatic System

Answer 8

Network of vessels that drains fluid, called lymph, that has escaped the blood from the capillaries and entered the surrounding tissues, also called interstitial space

Question 9

Immune System

Answer 9

Cells of the immune system travel between the circulatory system and the lymphatic system.

Some immune cells are in tissues and can directly interact with antigen when breach of barrier. Other mature immune cells travel within the blood to the site of infection, where they enter the tissues, and bind the antigen. Then enter the lymphatic system and travel to the lymph nodes, where the antigens are eliminated

Question 10

Lymphoid Organs (4 Major)

Answer 10

The immune and lymphatic systems share many of the same organs, called lymphoid organs.

4 major lymphoid organs:
1. thymus
2. spleen
3. liver
4. bone marrow

Question 11

Circulatory System

Answer 11

Where the lymph comes from and goes after being filtered. The lymphatic vessels, which are distributed throughout the body, pick up the lymph and carry it toward the heart, where it re-enters the circulatory system.

Question 12

Lymph definition

Answer 12

A colorless fluid containing white blood cells, that bathes the tissues and drains through the lymphatic system into the bloodstream

Question 13

Bone Marrow (structure, location, function)

Answer 13

Structure:
-Flexible tissue
-Divided in two types; yellow and red marrow
-Filled with hematopoietic cells* (Cells lodged within the bone marrow which are responsible for producing the cells which circulate in the blood (red blood cells, white blood cells, and platelets).

Location:
-Central cavity inside the bones

Function:
Red Marrow:
-Importance for the immune system
-Site of hematopoiesis* (origin of all immune cells, formation + differentiation of blood cells)
-Site of B-cell development

Yellow Marrow:
-Some leukocyte development
-Produces fat and cartilage

Question 14

Lymph Nodes (structure, location, function)

Answer 14

Structure:
-Small (1-25 mm)
-Bean-shaped
-Numerous (~600)
-Divided into three roughly concentric regions (cortex, paracortex, and medulla)
-Filled with lymphocytes*, macrophages, and dendritic cells
*Lymphocytes= white blood cells which arise from the lymphoid progenitor lineage during hematopoiesis. Generally refers to B- and T-cells

Location
-Grouped along the lymphatic vessels

Function:
-Filters the lymph
-Often it is the first organized lymphoid structure that foreign molecules encounter when first entering the body.

Question 15

MALT- Mucosal Associated Lymphoid Tissues (structure, location, function)

Answer 15

Structure:
-Refers to the combined surface area of various areas in the body including BALT, GALT, Lamina propria of intestinal villi, Peyer’s patches, tonsils, appendix
-Filled with various types of immune cells depending on the location.

Location:
-Mucous membranes lining the digestive, respiratory, and urogenital systems

Function:
-Initiates immune responses to specific antigens encountered along all mucosal surfaces

*BALT: Bronchus-associated lymphoid tissue; lymphoid structure part of the MALT located in lungs and bronchus.
*GALT: Gut-associated lymphoid tissue; lymphoid structure part of the MALT located in the gut.
*Lamina Propria of Intestinal Villi: Thin layer of connective tissue rich in immune cells located into the lumen of the small intestine.
*Peyer’s Patches: Small masses of lymphatic tissue found throughout the ileum region of the small intestine.
*Tonsils: Collection of lymphoid tissue facing the aerodigestive tract, mainly located into the pharynx.
*Appendix: A small, pouch-like sac of tissues located in the first part of the colon (cecum) in the lower-right abdomen. Harbours bacteria and aids in immune function. Recent research suggests that it plays a larger role in establishing the core gut microbiome than previously thought.

Question 16

Spleen (structure, location, function)

Answer 16

Structure:
-Large, ovoid
-Divided into two compartments; white pulp and red pulp.

Location:
-Situated in the left abdominal cavity

Function:
-Red pulp filters the blood
-White pulp is the site of development of immune responses against antigens found in the bloodstream

Question 17

Spleen: Red pulp vs. white pulp

Answer 17

White pulp is filled with macrophages, lymphocytes, T-cells, B-cells, and red blood cells. Red pulp is composed of cords of Billroth (consisting of fibrils and connective tissue cells with a large population of monocytes and macrophages) and splenic sinuses that are filled with blood. In the context of the immune system, white pulp is the important compartment of the spleen to remember as it is made of lymphatic tissue filled with immune cells.

Question 18

Thymus (structure, location, function)

Answer 18

Structure:
-Flat
-Bi-lobed; each lobe is divided into lobules which are organized each into two compartments (cortex and medulla)
-Filled with thymocytes* (T-cells found in the thymus), epithelial cells, dendritic cells, and macrophages

Location:
-Situated above the heart

Function:
-Site of T-cell development and maturation

Question 19

Primary Lymphoid Organs (2) + Functions

Answer 19

1. Thymus
2. Bone Marrow

Functions: site of lymphocyte maturation into an immunocompetent* cell

B-cell= bone marrow
T-cell= thymus

*immunocompetent= a mature lymphocyte that can recognize a specific antigen and mediate an immune response.

Question 20

Secondary Lymphoid Organs (3) + Functions

Answer 20

1. Spleen
2. Lymph nodes
3. MALT (mucosal associated lymphoid tissue)

Functions: site of lymphocyte activation into an effector cell* through interaction with trapped antigens

*effector cell= a mature lymphocyte that has been activated and mediates an immune response against a specific antigen

Question 21

Discrimination (Process)

Answer 21

Occurs through the ability of immune cells to distinguish between self and non-self components.

Almost every (nucleated) cell in the body expresses a molecule at their surface called Major Histocompatibility Complex class I (MHC I). This complex presents a “sample” of proteins found inside the cell. Another class of these MHC molecules (MHC II) are present on special cells of the immune system such as macrophages, dendritic cells and B-cells. Immune cells are then able to scan their area and recognize if there are abnormalities presented via the MHC protein. If abnormalities or foreign antigens (non-self) are detected, an immune response can be initiated.

Question 22

Elimination (4 steps)

Answer 22

Occurs through the ability of immune cells to initiate an immune response.

1. Pathogen (antigen) enters the body
2. Immune system recognizes the antigen
3. Activation of effector cell (innate and adaptive responses)
4. Elimination of the pathogen

Question 23

Innate Immune System (2 Components, 2 Functions)

Answer 23

-Consists of physical, soluble, and cellular barriers that are scattered throughout the body to prevent the entry of any infectious agent and respond non-specifically.

Components:
1. First line of defence against foreign agents.
2. Physical, soluble and cellular barriers.

Functions:
1. Immediate recognition and response to invading pathogens - response within minutes or hours.
2. Recognizes general patterns not specific for any one antigen; limits the type of immune response initiated.

Question 24

Adaptive Immune System (2 Components, 3 Functions)

Answer 24

Components
1. Humoral immunity (mediated by B-cells).
2. Cell-mediated immunity (mediated by T-cells).

Functions
1. Longer time required to initiate a response to invading pathogens - response within days.
2. Capable of recognizing and respond to specific antigens - its large diversity gives much wider range of responses that can be initiated.
3. Results in immunological memory - allows for a quick response upon a second infection with the same pathogen

Question 25

Innate vs. Adaptive

Answer 25

Innate:
-immunological memory not usually present
-small diversity of reactions possible
-non-specific (initiates similar reactions to all antigens)
-produces immediate reaction
-occurs within a few hours

Adaptive:
-immunological memory mostly present
-large diversity of reactions possible
-specific (initiates unique or antigen specific response to all antigens
-produces delayed reaction
-occurs within many hours to a few days

Both: Self/nonself discrimination

Question 26

What is the most ancient immune structure found in the evolution

Answer 26

The amebocyte* is one of the oldest types of cells that is believed to have given rise to a type of cell found in the human immune system today - the phagocyte!
Phagocytes are a type of cells that play a major role in the innate immunity. They have the ability to move by pseudopodia* and they can engulf free pathogens by phagocytosis*.