Immune response to microbial challenge

Question 1

Pathogens that infect via the respiratory tract

Answer 1

Influenza, RSV, M. Tuberculosis (TB), S. Pneumoniae, Cryptococcus

Question 2

Pathogens that infect via the faecal oral route

Answer 2

Hepatitis A, V. Cholerae, Shigella, E. coli

Question 3

Pathogens that infect via the sexually transmitted route

Answer 3

HIV, HPV, T. pallidum (Syphilis) N. gonorrhoeae, Candida albicans

Question 4

Pathogens that require a vector to infect

Answer 4

Rabies Virus, Plasmodium (Malaria), Schistosoma, Trypanosoma

Question 5

Mechanical mechanisms for preventing infection at Mucosal surfaces

Answer 5

Epithelial tight junctions

Longitudinal flow of air or fluid

Question 6

Chemical mechanisms for preventing infection at mucosal surfaces

Answer 6

Fatty acids (skin)
Enzymes: lysozyme, pepsin
Low pH
Antibacterial peptides
Mucus

Question 7

Microbiological mechanisms for preventing infection at Mucosal surfaces

Answer 7

Normal flora compete for nutrients/attachment sites

Production of antibacterial substances (colicins, E. coli)

Question 8

Examples of antimicrobial molecules

Answer 8

Lactoferrin
Lysozyme
Defensins

Question 9

Defence against pathogens in the lower respiratory tract

Answer 9

Mucosal surfaces
Lysozyme
‘Sweeping’ movement upward by ciliated epithelium
Antimicrobial peptides
Alveolar macrophages

Question 10

Defence against pathogens in the digestive system

Answer 10

Oral route – competition with well - adapted normal flora of mouth, intestine
Stomach - acid and secretions
Lower intestine – alkaline pH
Intestine - peristaltic action of intestine flushes out organisms
Pancreatic enzymes - bile salts, lysozyme

Question 11

Defence against pathogens in the genito-urinary system

Answer 11

Male system kept sterile
Female system colonised
Flushing mechanisms of urine
Acidity of urine
Vaginal epithelium – Lactobacillus acidophilus – acidic end products prevent colonisation

Question 12

How does MHC class I antigen presentation occur?

Answer 12

Peptides cleaved by proteasome
TAP transporter to ER
Assembled with MHC class I
Sent to Golgi complex
Sent to cell surface

Question 13

How do CD8+ lymphocytes kill infected cells?

Answer 13

Releasing granzymes and perforin or by engagement of Fas on target cells by Fas Ligand (FasL)
Secrete IFNy and TNFa

Question 14

Functions of antibodies

Answer 14

Lysis of membrane bound virus particles
Opsonisation of particles
Lysis of infected cells or pathogens 
Triggering of inflammation and immune cells
These functions often involve complement

Question 15

What does the membrane attack complex act upon?

Answer 15

Gram positive bacteria

Enveloped viruses

Question 16

Methods of passive immune evasion

Answer 16

Antigenic shift and drift leading to epitope escape
Anatomical seclusion/ hiding
Infection of immune cells

Question 17

Define antigenic drift

Answer 17

Small mutations in viral DNA accumulate over multiple replications, producing a closely related virus similar to the original

Question 18

Define antigenic shift

Answer 18

An abrupt, major change due to exchange of DNA between viral strains, producing a novel viral protein which the host has little protection against

Question 19

Methods of active immune invasion

Answer 19

Interference with innate system (e.g. affecting cytokines, Type I IFN, complement)
Interference with NK cells
Interference with the adaptive system (e.g. affecting MHC or antibodies)

Question 20

How HIV evades the immune system

Answer 20

Targets a key cell in adaptive immunity (CD4) and able to infect via APCs
Coat Proteins are covered in carbohydrates to evade recognition
Epitopes in gp41 are masked
RNA genome undergoes rapid change both CTL and antibody are evaded
Vaccination increases CD4 T cell infiltration to infected area, therefore increasing target cells

Question 21

What is most important in control of viruses?

Answer 21

Type I IFN, NK cells, CD8 cells

Question 22

What is most important in control of bacteria?

Answer 22

Antibody, Neutrophils, CD4 Cells

Question 23

What is most important in control of fungi?

Answer 23

CD4 Cells, Neutrophils

Question 24

What is most important in control of parasites?

Answer 24

Mast Cells, Eosinophils