Lecture 4 new

Question 1

Define the immune system:

Answer 1

Cells and organs that contribute to immune defences against infectious and non-infectious conditions (cancer)

Question 2

Define infectious disease:

Answer 2

When the pathogen succeeds in evading and/or overwhelming the host’s immune defences

Question 3

What is infectivity?

Answer 3

Ability of microorganisms to establish itself within the host or on the host

Question 4

What are the roles of the immune system?

Answer 4

PCRR
Pathogen recognition- cell surface and soluable receptors
Containing/eliminating infection (killing and clearance mechanisms)
Regulating itself- minimum damage to host, otherwise you develop autoimmune
Remembering pathogens- prevent the disease from recurring

Question 5

What are the two types of defence?

Answer 5

Innate immunity

• fast
• lack of specificity
• lack of memory
• no change in intensity

Adaptive immunity

• slow
• specific
• immunologic memory
• changes in intensity

Question 6

What are the 1st line defences? (innate immunity)

Answer 6

Barriers to stop pathogen entering

• physical barriers
• physiological barriers
• chemical barriers
• biological barriers

Question 7

What are the physical barriers?

Answer 7

• skin
• mucous membranes of mouth/ resp tract/ GI tract/ urinary tract
• bronchial cilia (beat to expel trapped microbes in mucous)

Question 8

What are the physiological barriers?

Answer 8

• diarrhoea (food poisoning)
• vomiting (food poisoning/hepatitis/meningitis)
• coughing (pneumonia)
• sneezing (sinusitis)

Question 9

What are the chemical barriers?

Answer 9

Low pH: skin 5.5, stomach 1-3, vagina 4.4
Antimicrobial molecules:
-IgA (tears/saliva/mucous membrane)
-lysozyme (sebum/perspiration/urine)
-mucous (mucous membrane)
-beta-defensins (epithelium)
-gastric acid and pepsin (endopeptidase)

Question 10

What are biological barriers?

Answer 10

Normal flora

-non pathogenic microbes (found in nasopharynx, mouth, throat, skin, GI tract, vagina)

Question 11

Where are normal flora absent?

Answer 11

In internal organs/tissues

Question 12

What are the benefits of normal flora?

Answer 12

-compete with pathogens for attachment sites and resources
-produce antimicrobial chemicals
-synthesise vitamins K, B12, and other B vitamins
-immune maturation
(normal flora can become pathogenic)

Question 13

Give some examples of normal flora that inhabit the skin:

Answer 13

• staphylococcus aureus
• staphylococcus epidermidis
• streptococcus pyogenes
• candida albicans
• clostridium perfringens

Question 14

Give some examples of normal flora that inhabit the nasopharynx:

Answer 14

• streptococcus pneumoniae
• neisseria meningitidis
• haemophilus species

Question 15

How is normal flora displaced from its normal location?

Answer 15

Breaching skin integrity

• skin loss (burns)
• surgery
• IV lines
• skin diseases
• injection drug users
• tattooing/body piercing

Fecal-oral route
-foodbourne infection

Fecal-perineal-urethral route
-UTI in women

Poor dental hygiene/dental work

• dental extraction
• gingivitis (gum disease)
• brushing/flossing

Question 16

What is the perineum?

Answer 16

The space between the anus and scrotum in the male and between the anus and the vulva in the female

Question 17

What are some high risk patients susceptible to serious infections?

Answer 17

• asplenic/hyposplenic patients
• patients with damaged/prosthetic valves
• patients with previous infective endocarditis (infection of of the endocardium- the inner lining of the heart)

Question 18

What may cause normal flora to overgrow and become pathogenic when host is immunocomprimised?

Answer 18

• diabetes
• AIDS
• malignant diseases
• chemotherapy

Question 19

What conditions cause the flora in mucosal surfaces to be depleted by antibiotic therapy?

Answer 19

• severe colitis (intestine): clostridium difficile

- thrush (vagina): candida albicans

Question 20

What are the second lines of defences that contain and clear the infection?

Answer 20

• phagocytes
• chemicals
• inflammation

Question 21

What are the main types of phagocytes?

Answer 21

• macrophages
• monocytes
• neutrohpils (pus)

Question 22

What is the function of a macrophage?

Answer 22

• present in all organs
• ingest and destroy microbes via phagocytosis
• present microbial antigens to T cells
• produce cytokines/chemokines

Question 23

What is the function of monocytes?

Answer 23

• present in blood

- recruited at infection site and differentiate into macrophages

Question 24

What is the function of neutrophils?

Answer 24

• present in blood (60% of blood leukocytes)
• increased during in infection
• recruited by chemokines to site of infection
• ingest and destroy pyogenic bacteria (Staph. aureus, Strep.pyogenes)

Question 25

What is a pyogenic bacteria?

Answer 25

Bacteria which produces pus

Question 26

What is the function of basophils/mast cells? (granulocytes)

Answer 26

• early actors of inflammation (vasomodulation)

- important in allergic responses

Question 27

What is the function of eosinophils?

Answer 27

Defence against multi-cellular parasites (worms)

Question 28

What is the function of natural killer cells?

Answer 28

Kill all abnormal host cells (virus infected or malignant)

Question 29

What is the function of dendritic cells?

Answer 29

Present microbial antigens to T cells

Question 30

How are pathogens recognised?

Answer 30

Microbial structures: PAMPs (pathogen associated molecular patterns) e.g. carbohydrates/lipids/proteins/nucleic acids

Phagocytes: PRRs (pathogen recognition receptors)

(PRRs allow phagocytic cells to detect PAMPs)

Question 31

Give an example of a PRR:

Answer 31

TLR (toll like receptor)- these bind to various PAMPs and communicate with the nucleus of the phagocyte to ellicit a response

Question 32

What is opsonisation of microbes?

Answer 32

Opsonins are coating proteins which bind to the microbial surfaces leading to enhanced attachment of phagocytes and therefore clearance of molecules

Question 33

Give some examples of opsonins:

Answer 33

Complement proteins: C3b/C4b

Antibodies: IgG/IgM (these attach to antigens on the microbe which in turn acts as an opsonin for the opsonin receptor on the phagocyte)

Acute phase proteins: CRP (C-Reactive protein)/ MBL (mannose-binding lectin)

Question 34

How do phagocytes work?

Answer 34

• recognition (PAMPs & opsonins)
• engulfment
• degradation of infectious microbes

Question 35

What are the 2 intracellular killing mechanisms of a phagocyte?

Answer 35

1) oxygen dependent pathway (respiratory burst: using oxygen free radicals)
2) oxygen independent pathways (lysozyme)

Question 36

What is the system of phagocytosis?

Answer 36

• chemotaxis and adherence of microbe to phagocyte
• ingestion of microbe by phagocyte
• formation of phagosome (phagocytic vesicle)
• fusion of phagosome with lysosome to form phagolysosome
• digestion of ingested microbe by enzymes
• formation of residual body containing indigestible material
• discharge of waste materials

Question 37

Why are you at risk of infection when you have a splenectomy?

Answer 37

The spleen clears encapsulated bacteria such as: Neisseria meningitidis/Streptococcus pneumoniae/Haemophilus influenzae B

Question 38

What is the complement system?

Answer 38

20 serum proteins

the most important are C1-C9

Question 39

Give some examples of complements with antimicrobial actions:

Answer 39

They float around in blood. and become activated in presense of pathogen.
C3a/C5a recruit phagocytes
C3b/C4b for opsonisation of pathogens
C5-9: Killing of pathogens & Membrane attack complex (MAC forms transmembrane channels which disrupt the cell membrane of target cells causing lysis and death)

Question 40

How do cytokines act?

Answer 40

• chemoattraction
• phagocyte activation
• inflammation