Introduction to the Immune System

Question 1

Define the roles of the Immune System

Answer 1

1. Defense against infection
2. Defense against tumors
3. Injure cells and induce pathologic inflammation
4. Recognizes and responds to tissue grafts and newly introduced proteins

Question 2

Define Adaptive Immunity

Answer 2

Response of Ag-specific lymphocytes to Ag includes MEMORY

Question 3

Define Innate Immunity

Answer 3

Protection against Ag that relies on mechanisms that exist before exposure

Question 4

What is CD?

Answer 4

Cluster of Differentiation

Cell surface molecules expressed on various cell types are designated by a CD number

Question 5

CDs to memorize

Answer 5

CD21 = CR2 = C3dR
CD25 = IL-2Ra
CD152 = CTLA4
CD95 = Fas

Question 6

Define Cytokines

Answer 6

Molecules that tell other cells what to do, mediate the immune response
They act through autocrine, paracrine, and exocrine actions.
Pleiotropic and redundant
They include: IL, TNF, IFN-a/B/y, TGF-B, CSF

Question 7

Define Chemokines

Answer 7

They tell other cells to come here. 
Chemotatic cytokine (IL-8)

Question 8

Define Immunogen

Answer 8

Ag that evokes a specific immune response

Question 9

Define Tolerogen

Answer 9

Ag that induces immunologic tolerance

Question 10

Define Endogenous Ags

Answer 10

Body’s own cellular components or intracellular pathogens

Question 11

What are the different classifications of endogenous Age?

Answer 11

Autoantigens: SELF-Ag

Alloantigens: Tissue specific Ag, which is present in one individual but not another

Intracellular pathogens: Viruses, parasites, intracellular bacteria

Question 12

Define Exogenous Ags

Answer 12

Ags that enter body or system, freely circulate in body fluids and are trapped by APCs

Uptake of Exo Ags by APCs mediated by phagocytosis

Question 13

What structures make up Innate Immunity?

Answer 13

Epithelial Barriers, Mast Cells, Phagocytes, Dendritic Cells, Complement, NK cells and ILCs

Question 14

What structures make up Adaptive Immunity?

Answer 14

B-lymphocytes (which may become Plasma cells)

T-lymphocytes (T-helpers, Cytotoxic T, Tregs, NK cells)

Question 15

What are the Characteristics of Innate Immunity?

Answer 15

Respond rapidly 
Normally inactive in absence of infection 
Found in ANY vascular tissue 
Limited diversity 
NO Memory 
Stimulates Adaptive Immunity

Question 16

What cell types are Phagocytes?

Answer 16

Neutrophils
Monocytes/Macrophages
Dendritic Cells

Question 17

What are some characteristics of Neutrophils?

Answer 17

AKA: polymononuclear 
Circulate, short-lived
First at Site of Infection 
Make up 54-62% of WBCs
Component of pus (pyogenic)

Question 18

CD marker for Neutrophil

Answer 18

CD15, CD16b

Question 19

_1__ is present in the bloodstream and turns into _2__ in tissues. What phagocytes fill in the blanks?

Answer 19

1. Monocytes

2. Macrophages

Question 20

What are some characteristics of Monocytes/Macrophages (MO)?

Answer 20

Respond to site of inflammation in 1-2 days
Survive longer than neutrophils
Levels increased in chronic inflammation, immune-mediated diseases, stress, and necrosis

2 Major functions by:
M1 classical MO
M2 alternative MO

Question 21

Define M1 classical macrophages.

Answer 21

They are induced by innate immunity to play a role in INFLAMMATION.

Question 22

Define M2 alternative macrophages.

Answer 22

They are induced by IL-4 and IL-13 to play a role in TISSUE REPAIR and CONTROL of INFLAMMATION.

Question 23

Other functions of MOs at various stages include?

Answer 23

Garbage collectors ("resting" state)
Ag presenting cells ("activated" state) 
Vicious killers ("Hyperactivated" state)

Question 24

CD marker for MOs

Answer 24

CD14 (TLR4)

Recognizes and binds to LPS

Question 25

What are some characteristics of Dendritic Cells? | **Include surface expression and CD marker**

Answer 25

Professional APCs Capture Ag, migrate to lymphoid tissue and present Ag to mature, naive T cells Express: High levels of Class II HLA/MHC and CD80 (B7) *May also present Ag with Class I HLA/MHC

Question 26

What is significant about dendritic cells expressing high levels of Class II HLA/MHC + CD80?

Answer 26

It makes Dendritic cells better APCs than Macrophages and B-cells.

Question 27

What is the major function of APCs?

Answer 27

They are the bridge b/w innate and adaptive immunity.

Question 28

Define Specific Immunity.

Answer 28

Distinguish b/w different, closely related, microbes and molecules

Question 29

Define Acquired Immunity.

Answer 29

Potent protective responses are "acquired" by experience

Question 30

Characteristics of Adaptive Immunity

Answer 30

Specific for Ag Diverse - receptors are produced by somatic recombination of gene segments Has Memory

Question 31

What are some characteristics of Eosinophils?

Answer 31

Differentiate in response to IL-5 Responsible for combating multi-cellular parasites Major role in atopic diseases

Question 32

What are some characteristics of Basophils?

Answer 32

Bi-lobed nucleus Release pharmacologically active substances contained within granules Role in Atopic diseases Combat parasitic diseases

Question 33

What are some characteristics of Mast Cells?

Answer 33

2 types: tissue and mucosal Can be stimulated to degranulate by direst injury, chemicals, alcohols, and certain Abs, cross linking of IgE receptors, or activated C' proteins Key role in inflammatory process Atopic responses

Question 34

CD marker for Mast cells

Answer 34

CD23

Question 35

Mature, Naive vs. Effector vs. Memory lymphocytes

Answer 35

Naive is when It has not been activated by Ag yet. Effectors have been activated by Ag Memory lymphocytes remember that you have immunity to a pathogen.

Question 36

Humoral vs. Cell-mediated Immunity

Answer 36

Humoral - Antibodies neutralize and eradicate exogenous Ags (B-cells, produce immunoglobulins) Cell-mediated - Activation of cell to eradicated endogenous antigens (T-cells)

Question 37

Function of Effector B-cells | CD marker?

Answer 37

Neutralization of microbe Phagocytosis Complement activation CD19, CD21

Question 38

Function of Helper T-cells | CD marker?

Answer 38

Activation of macrophages Inflammation Activation (proliferation and differentiation) of T and B lymphocytes CD3, CD4 Th1: IL-2, IFN-y Th2: IL-4, IL-5, IL-13 Th17: IL-17, IL-22

Question 39

Function of Cytotoxic T-cells | CD marker?

Answer 39

Killing of infected cells | CD3, CD8

Question 40

Function of Regulatory T-cells | CD marker?

Answer 40

Suppression of Immune Response | CD3, CD4, CD25, IL-10, TGF-B

Question 41

How does the Lymphatic system work?

Answer 41

It drains the tissues and transports lymphocytes and antigens to secondary lymphoid tissue, where the lymphocytes can interact with the antigens. As blood is circulating, some fluid leaks out of the capillaries. This fluid is lymph. Most of the fluid will return back to the circulatory system through one way valves into the lymphatic vessels. Lymph moves via muscle movement.

Question 42

What occurs in the lymphoid tissue?

Answer 42

Dendrites or APCs will enter the lymphoid tissue through the Afferent lymphatic vessels. Lymphocytes will enter through the high endothelial venues. They follow lymphocyte specific chemokine to different regions of tissue (different zones for B and T cells). There they are activated by an APC and leave through the circulatory system. If they are not activated they leave through the Efferent lymphatic vessels and go to the next lymphoid tissue. They will eventually end up at the thoracic duct and go back into circulation.

Question 43

Function of Natural Killer Cells in Innate Immunity | CD marker?

Answer 43

Recognize infected, stressed, or malignant cells and kill them by releasing granzymes and perforins leading to apoptosis of target cell Activated by IL-12, IL-15, and Type 1 IFNs Activated NKs secrete IFN-y (activates macrophages) CD16, CD56

Question 44

What is the difference b/w NK cells and Cytotoxic T cells?

Answer 44

NK cell don't recognize specific antigens like cytotoxic T cells do.

Question 45

What is the relationship b/w NK cell and macrophages?

Answer 45

NK cells are activated by IL-12, which are release by macrophages. NK cells will then release IFN-y, which hyperactivates macrophages. Macrophages will then produce more IL-12, activating more NKs... and so on.

Question 46

What is a primary immune response?

Answer 46

It is the first time an Ag is encountered. Activation of naive cells to perform effector functions Generation of memory cells

Question 47

What is a secondary immune response?

Answer 47

It is the second time an Ag is encountered. Memory cells are activated There is a stronger, faster effector response

Question 48

Describe the Mucosal Immune System.

Answer 48

Largest SA as barrier against outside world More bacterial DNA than human Microbiome - part of innate immune system Contains very specialized cells and responses for protection IgA - Ab abundantly produced in mucosal tissue, bind/neutralizes microbes

Question 49

Define the Cutaneous Immune System.

Answer 49

SKIN - second largest barrier Has specialized innate and adaptive cells and responses Langerhans - primary APC in epidermis

Question 50

Phases of Adaptive Immune Response

Answer 50

Antigen Recognition (T cells activated by APCs, B cells by Antigens) Lymphocyte Activation (Clonal expansion and differentiation of lymphocytes - Ab producing cells and effector cells) Antigen Elimination (by Abs and effector Ts) Homeostasis (Apoptosis of infected cells) Memory (surviving memory cells)

Question 51

Describe Systemic Immunity.

Answer 51

Lymphocytes travel to secondary (peripheral) lymphoid organ where they will come into contact with antigens that traveled from site of infection via lymph. Antigens also travel to the spleen via blood. Activation of lymphocytes and initiation of adaptive immune responses. Effector Ts and Abs migrate to site of infection.

Question 52

Define Active Immunity.

Answer 52

Introduction of an Ag that provokes an adaptive immune response. Has memory! ``` Artificial = vaccine Natural = infection ```

Question 53

Define Passive Immunity.

Answer 53

Introduction of Ab or antiserum into naive recipient No memory! ``` Artificial = IVIG (intravenous immunoglobulin) Natural = maternal ```

Question 54

What are the Primary lymphoid organs? Secondary?

Answer 54

``` Primary = Bone marrow and Thymus Secondary = Spleen, Lymph node, mucosal immune tissue ```

Question 55

Describe the time line for Innate and Adaptive Immunity.

Answer 55

Phase 1 (0-4 hrs) = Non-induced Innate - skin, pH, saliva Phase 2 (4-96 hrs) = Induced Innate, broadly specific - phagocytosis, C' system, inflammation, cytokines Phase 3 (>96 hrs) = Induced Adaptive, highly specific - B cells (Ab), helper Ts, CytT

Question 56

Circulatory immune cells vs. Tissue immune cells

Answer 56

Circulatory = Neutrophils, Eosinophils, Basophils, Monocytes, T/B/NK cells, platelets, RBCs Tissue = Tissue eosinophil, Mast cell, Macrophage, T-lymphocyte, Plasma cell, NK cell

Question 57

Describe the migration of T and B lymphocytes in secondary lymphoid tissue.

Answer 57

Naive T-cells enter through high endothelial venules Adhesion molecules used by Ts to bind to endothelium constitutively expressed Chemokines produced in T-cell zones bind to chemokine receptor CCR7 on naive T-cells Chemokine interaction with CCR7 causes T-cells to bind tightly to HEVs Naive Ts migrate to T-cell zone Naive B = similar Migrate to LN follicles being guided by chemokines that bind to CXCR5 receptor on B cells