Cornea Lectures

Question 1

What are the two main divisions of the human immune system?

Answer 1

Innate immunity

Acquired (cell-mediated, humoral) immunity

Question 2

What are the key characteristics of the innate immune system in terms of line of defence, mobilisation and pathogen exposure?

Answer 2

1st line of defence
Rapidly mobilised
No prior pathogen exposure needed

Question 3

Does the innate immune system target specific pathogens? Which pathogens evade this system?

Answer 3

Non-specific

Intracellular pathogens not lysed

Question 4

What physical barriers are in place to prevent pathogen entry? Which chemicals are produced in response to attempted entry?

Answer 4

Skin, eyelids, tears

Antibodies (from B cells), cytokines

Question 5

What are the fluid and protein components of the innate immune system?

Answer 5

Blood, aqueous humor

Complement, mannose-binding lectin, lysozymes, anti-proteases

Question 6

How does the complement cascade respond to detecting antigens?

Answer 6

Binding to antibodies

Question 7

What is the action of lysozymes and what enzymes counteract their effect?

Answer 7

Lysing invading pathogens

Counteracted by anti-proteases

Question 8

Which cells make up the innate immune system?

Answer 8

Phagocytes

Cytotoxic cells: Leucocytes, macrophages, natural killer cells

Question 9

Which cells of the innate immune system are primary scavengers? What is their action?

Answer 9

Neutrophils

Attracted to inflammation sites by cytokines, release free radicals and proteases

Question 10

What are the two main antigen-presenting cells in the innate immune system?

Answer 10

Macrophages (MHC class II)
Dendritic cells

Question 11

What are the main functions of macrophages?

Answer 11

Cell lysis, clearing antigen-coated cells
Active lymphocytes via cytokines
Trigger acquired immunity via lymphoid tissue

Question 12

Where are dendritic cells of the innate immune system most often found?

Answer 12

High exposure sites: Respiratory system, digestive tract

Question 13

After working on tissues where do dendritic cells recirculate to?

Answer 13

Lymph nodes

Spleen

Question 14

Name a type of dendritic cell and where it can be found.

Answer 14

Langerhans cell

Skin, conjunctiva, cornea (stroma)

Question 15

How does acquired immunity differ from innate immunity?

Answer 15

Antigen-specific
Forms immunological memory
Defends against both intracellular and extracellular pathogens

Question 16

How do memory cells improve subsequent immune responses to the same invading pathogens?

Answer 16

Somatic mutations alter antibody, allowing better antigen recognition

Question 17

Which cells make up the acquired immune system?

Answer 17

Lymphocytes
T cells, B cells
Natural killer cells

Question 18

What are the functions of lymphocytes?

Answer 18

Recognise foreign antigens on pathogens and secrete cytokines

Question 19

Which cells are activated by T cells and produce antibodies in acquired immunity? What do they do?

Answer 19

B cells

Counteract foreign antigens, activate other cells

Question 20

Which polymorphic cells recognise antigens presented by MHC?

Answer 20

T cells

Question 21

Which MHC classes do T helper cells and cytotoxic/suppressor T cells respond to respectively?

Answer 21

T helper cells: MHC class II
Cytotoxic/suppressor T cells: MHC class I

Question 22

How do cytokines affect macrophages, B and T cells?

Answer 22

T and B cells proliferate

Macrophages are activated

Question 23

What do MHC classes determine?

Answer 23

Whether pathogen is intracellular or extracellular

Question 24

Which antibodies are seen in the: (a.) Initial immune response, (b.) Secondary immune response, (c.) Mucosal immune system (e.g. tears)?

Answer 24

(a. ) IgM
(b. ) IgG
(c. ) IgA

Question 25

Which circulating granulocytes do not need prior activation in acquired immunity?

Answer 25

Natural killer cells

Question 26

Which cells are natural killer cells effective against? How do they destroy targets?

Answer 26

Tumour cells, virus-infected cells | Direct contact, antibodies

Question 27

What are the phases of the immune response?

Answer 27

1. Afferent phase 2. T cell activation 3. Effector phase 4. Secondary response

Question 28

What takes place in the afferent phase of the immune response?

Answer 28

Foreign antigen taken from entry site, presented to lymphocytes in lymphoid tissue by APC's

Question 29

What do activated T cells do?

Answer 29

Produce cytokines | Stimulate cells to become cytotoxic

Question 30

What takes place in the efferent phase of the immune response?

Answer 30

T cells induce cytotoxic T cells, B cells and macrophages to remove antigen Antigen-specific B and T cells appear

Question 31

How does the secondary immune response differ from the initial one?

Answer 31

More antigen-specific B and T cells recruited quicker | Type and specificity of antibody differs

Question 32

What do dendritic cells do?

Answer 32

``` Pinocytosis in ECM Lyses cells in acidic vacuole, puts their antigens on surface via MHC class II ```

Question 33

Which immune cells recognise MHC class I (found in all cells) and for which antigens?

Answer 33

``` CD8 cytotoxic T cell Intracellular antigens (viral, self) ```

Question 34

Which immune cells (a.) present, (b.) recognise MHC class II and for which antigens?

Answer 34

(a.) Macrophages, dendritic cells (b.) CD4 helper T cell Extracellular antigens (bacteria, fungi)

Question 35

What are the key characteristics of T cell receptors?

Answer 35

Unique to every T cell to recognise different antigens | via embryonic gene rearrangment

Question 36

Which are the most important cytokines for T cells? Which one is lost in proliferation?

Answer 36

IL-2, 4, 7 | IL-2 lost (activated cytotoxic T cells)

Question 37

What are the key characteristics of B cell receptors?

Answer 37

Unique immunoglobulin surface antigen receptor Excreted as soluble antibody Marks foreign antigens recognised by identical T cell receptor for removal by innate immunity

Question 38

What is the first stage of the antibody response?

Answer 38

Antigen broken up Picked up by APC and processed Presented to T helper cell

Question 39

What is the second stage of the antibody response?

Answer 39

B cell picks up antigen via antibody, more processing | Activated to divide

Question 40

What is the third stage of the antibody response?

Answer 40

Antibody-forming cells produce soluble antibody | Some remain on B cell surface membrane

Question 41

What is the initial immune response to injury and infection?

Answer 41

Inflammation | Pathogen removal by innate immune system

Question 42

Why are immune cells attracted to the injury site?

Answer 42

Tissue component changes (blood vessels, ECM)

Question 43

How is acquired immunity activated following injury?

Answer 43

Degraded pathogen antigen transported to lymphoid tissue

Question 44

What is seen in the first stage of the injury and infection response at the site?

Answer 44

Vascular leaks | Leucocyte activation, adhesion, migration

Question 45

What occurs after antigen migration in the first stage of the injury and infection response?

Answer 45

Acquired immune system activation in the lymphoid tissue | Inflammation

Question 46

What is seen in the second stage of the injury and infection response?

Answer 46

Phagocytosis | ECM changes

Question 47

What is seen in the third stage of the injury and infection response?

Answer 47

Inflammation resolution | Tissue remodeling

Question 48

What is the definition of immune privilege?

Answer 48

The ability to tolerate the introduction of antigens without eliciting an inflammatory immune response

Question 49

Which bodily organs demonstrate immune privilege?

Answer 49

``` Brain Ovaries Testes Pregnant uterus Placenta Eye ```

Question 50

Which factors affect immune privilege?

Answer 50

Avascularity, blood ocular barrier (iris, ciliary body, retina) Local immunosuppressive neuropeptides, cytokines Less MHC expression, class II APC's, Langerhans cells Anterior chamber associated immune deviation, apoptosis

Question 51

Which immunosuppressive factors are in the aqueous humor?

Answer 51

TGF-beta, alpha-MSH VIP, CGRP, cortisol NK Cell Inhibitory Factor Soluble Fas ligand

Question 52

What role does TGF-beta play in the immune response?

Answer 52

Inhibits B/T cell proliferation IL-2 receptor expression Antibody production

Question 53

What role does alpha-MSH play in the immune response?

Answer 53

Suppresses pro-inflammatory cytokines (IFN-gamma, IL-1, TNF-alpha)

Question 54

What role does VIP play in the immune response?

Answer 54

Inhibits IL-2 to suppress lymphocyte proliferation

Question 55

What role does CGRP play in the immune response?

Answer 55

Inhibits delayed-type hypersensitivity

Question 56

What role does NK Cell Inhibitory Factor play in the immune response?

Answer 56

Protects corneal endothelium from attack by NK cells

Question 57

What role does the soluble Fas ligand play in the immune response?

Answer 57

Downregulates inflammatory cytokines (IFN-gamma, IL-1, TNF-alpha) Kills active lymphocytes

Question 58

What does ACAID stand for? Which intact organs are required?

Answer 58

Anterior chamber associated immune deviation | Eye, spleen

Question 59

Which cells begin the process of ACAID? How do they do so?

Answer 59

Dendritic cells | Antigen presentation via the lymphatic system

Question 60

Which two processes occur in ACAID?

Answer 60

Antibody response induction | Suppression of delayed type hypersensitivity

Question 61

How is ACAID triggered?

Answer 61

TGF-beta (aqueous humor, tears) APC response Thrombospondin

Question 62

What phases are involved in ACAID?

Answer 62

Ocular phase Splenic phase A Splenic phase B

Question 63

How is the ocular phase of ACAID carried out?

Answer 63

Antigen in anterior chamber captured by indigenous APC's

Question 64

Where does the antigen travel to in the ocular phase of ACAID?

Answer 64

Trabecular meshwork to blood to marginal zone of spleen