5. Immunity& Disease

Question 1

Why do you need to know?

Answer 1

Affects all patients
Infections common
Some patients more susceptible to infection
Some medical conditions caused directly by the immune system

Question 2

What is Immunity?

Answer 2

Protection or defence against infections…
BACTERIA
VIRUS
FUNGI
Toxins 
Cancer

Question 3

Immune System

Answer 3

Distinguishes self from non-self molecules

Activates multiple mechanisms to either eliminate or neutralise threat
2 main pathways
Innate
Adaptive

Question 4

Defence against disease

Answer 4

Innate immunity

Adaptive immune reponse

Question 5

Innate immunity

Answer 5

Defense mechansims present even before infection or activated in a non-specific way
Skin, mucous membranes
Phagocytic cells (neutrophils, macrophages), inflammation, fever

Question 6

Adaptive immune reponse

Answer 6

Cell-mediated immunity

Humoral immunity

Question 7

Non-specific defences

Answer 7

Non-specific defenses are designed to prevent infections by viruses and bacteria
These include:
Intact skin
Mucus and Cilia

Question 8

Skin

Answer 8

Outer layer of keratin – mechanical barrier
Dead skin cells constantly sloughed off
hard for invading bacteria to colonize
Sweat and oils contain anti-microbial chemicals

Question 9

Mucous membranes

Answer 9

Normal flow of mucus washes bacteria and viruses off of mucus membranes
Cilia (hair-like projections on cells) – respiratory tract
Acid – stomach, vagina
Enzymes – saliva, eye

Question 10

Chemical barriers

Answer 10

Proteins
Complement - works with other defence mechanisms of the body
Interferons - inhibit the replication of many viruses

Question 11

Cellular defences - phagocytosis (1)

Answer 11

Granulocytes
Neutrophils, eosinophils, basophils
Remove dead cells and micro-organisms
Attracted by an inflammatory response of damaged cells

Question 12

Cellular defences - phagocytosis (2)

Answer 12

Monocytes
macrophages
In tissues which serve as filters for trapping microbes
Macrophages live longer than granulocytes
Attracted by different stimuli and usually arrive at sites of invasion later than granulocytes
Stimulate specific immune response (‘antigen-presenting’)

Question 13

Non-specific responses to infection

Answer 13

-Macrophages release protein signals
interleukin-1 (IL-1) and interleukin-6 (IL-6)
-Fever
Most bacteria grow optimally at temp below body temp
-Pain, swelling, redness
Increasing capillary permeability, promoting blood flow, bringing more phagocytic cells
-Acute-phase proteins released from liver
Bind to bacteria and activate complement proteins

Question 14

Specific (adaptive) immunity

Answer 14

Relies on antigens
specific substances found in foreign microbes
Lymphocytes
Can travel swiftly around the body when carried along in the blood or lymph
Approx 2 x 10^12 lymphocytes in human body
Approx 1 % are in the bloodstream
Rest in lymphatic system

Question 15

Lymphocytes (1)

Answer 15

Produced in bone marrow
B-cells mature in bone marrow then concentrate in lymph nodes and spleen
T-cells mature in thymus
B and T-cells mature then circulate in the blood and lymph
Circulation ensures they come into contact with pathogens and each other

Question 16

Lymphoid tissues

Answer 16

Adenoid
Tonsil
Thymus
Spleen
Appendix
Bone Marrow
Lymph Nodes
Peyers Patch (small intestine)
Lymphoid aggregates (large intestine)
Lymphatics

Question 17

Lymphocytes (2)

Answer 17

B-cells

T-cells

Question 18

B-cells

Answer 18

Secrete antibodies
Humoral immunity
Recognise pathogens outside cells

Question 19

T-cells (1)

Answer 19

Do not recognise free antigen - only recognise antigen presented by major histocompatibility complex – class I (all cells) or class II (APC)
Directly attack invaders (cytotoxic, CD8+, MHC I)
Cell-mediated immunity
Recognise pathogens that have entered cells
Also help B-cells (helper cells, CD4+, MHC II)

Question 20

T-cells (2)

Answer 20

Cytotoxic

Helper

Question 21

Cytotoxic

Answer 21

Seek out and destroy any antigens in the system, and destroy microbes “tagged” by antibodies
Some cytotoxic T-cells can recognize and destroy cancer cells
Variable region on T-cell receptor

Question 22

Helper

Answer 22

Stimulate B-cells

Activate cytotoxic - cells and macrophages to attack infected cells

Question 23

How do T-cells recognise an invader?

Answer 23

Detect antigen – protein marker on cell surface
(Epitope = fragment of antigen)

If an antigen (“not self”) protein is encountered by a macrophage, it will bring the protein to a helper T-cell for identification.

If the helper T-cell recognizes the protein as “not self,” it will launch an immune response.

Question 24

Signalling immune response

Answer 24

Helper T-cells (CD4+) stimulated by antigen  cytokines to stimulate B-cell division

HIV destroys helper T-cells so immune response diminished

Question 25

B-cells (2)

Answer 25

Produce antibodies
Glycoproteins
Specific, hypervariable region
Different subtypes IgG, IgM, IgA, IgE, IgD
Opsonisation, bind and block (agglutinate), stimulate complement
Bind to antigen on cell or free  plasma cells  more antibody
Or become memory cells - remain ready to divide rapidly if an invasion occurs again

Question 26

Immune System

Answer 26

Vital for survival but can be a double-edged sword
Immunodeficiency – prone to infections
Overactive immune system- hypersensitivity reactions
Failure to recognise self- autoimmune diseases

Question 27

The Immune System - Deficient

Answer 27

Chemotherapy / Drugs
HIV
Splenectomy
Bone Marrow dysfunction

Question 28

The Immune System - Hyperactive

Answer 28

Allergy (Hypersensitivity)
Auto-immunity
Overreaction to Pathogen

Question 29

Immunodeficiency (1)

Answer 29

Drugs
Chemotherapy
Immunosuppressive Medication 
Splenectomy
Bone Marrow Dysfunction

Question 30

Immunodeficiency (2)

HIV – Human Immunodeficiency Virus

Answer 30

Retrovirus
- Infects CD4+ T cells
- causes AIDS (Acquired Immunodeficiency Syndrome)
Stages of progression : Infection, Latency, AIDS
AIDS - decline in CD4+ T-cells, opportunistic infections

Question 31

Immunodeficiency (3)

Answer 31

Important to know if a patient is immunosupressed
More prone to infection
Significantly alter the immune response of the patient to infection

Question 32

Causes of secondary immunodeficiency

Answer 32

Malnutrition
Burns
Uremia
Diabetes mellitus
Immunotoxic medications
Self-medication of recreational drugs and alcohol
AIDS

Question 33

Hyperactive (1)

Answer 33

Hypersensitivity
Excessive immune reaction against harmless antigen.
Type 1 – Type 4 – based on mechanism.
Type 1 – Anaphylaxis/Allergy
e.g. Asthma, Rhinitis (Hay fever), Peanut allergy.
- Sensitization first step.

Question 34

Hyperactive (2)

Answer 34

Over reaction to pathogen

Systemic Inflammatory Response Syndrome

Question 35

Hyperactive (3)

Answer 35

Autoimmunity
failure of an organism in recognizing its own constituent parts as self
leading to an immune response against its own cells and tissues

Normally display “self tolerance”
Self reactive lymphocytes
deleted centrally
suppressed in periphery

Question 36

Autoimmune Diseases

Answer 36

Type 1 Diabetes Mellitus
Coeliac Disease
Multiple Sclerosis
Hashimoto’s Thyroiditis

Question 37

Manipulation of Immune System

Answer 37

Suppress Immune system
Organ transplant
- increased susceptibility to infection

Cancer – Immunotherapy

Vaccination

Question 38

Vaccination (1)

Answer 38

= Active Immunity
Stimulate own immune system to elicit adaptive immune response, prevent future infection.

Success depends on Herd Immunity

Question 39

Vaccination (2)

Answer 39

Live (Attenuated) Vaccines - live, weakened pathogen
e.g. MMR
Inactivated Vaccines - inactivated, part of pathogen
e.g. Hepatitis B
Toxoid - bacterial toxin
e.g. Diptheria
Conjugated - antigen linked to protein carrier
e.g. Pneumococcal