Microbial immune evasion mechanism

Question 1

What is balanced pathogenictiy?

Answer 1

Question 2

What are bacterial virulence factors?

Answer 2

Proteins produce by bacteria to infect and cause disease

1. Promote colonisation and adhesion - to establish infection = adhesins
2. Toxins aid growth and transmission
3. Evade host defences
4. Promote tissue damage

Question 3

What aspect of immunity have pathogens evolved to overcome or avoid?

Answer 3

Reaching through natural defences - mucosal layers, skin

Innate immunity - altering complement system, affect the ability of macrophages to phagocytose

Adaptive immunity - antigen specific and memory antibodies T cells - alter ability of CD4 helper cells and CD8 cytotoxic cells

Question 4

What are the roles of the complement?

Answer 4

• Induce inflammatory response
• Promote chemotaxis
• Increase phagocytosis by opsonisation
• Increase vascular permeability
• Mast cell degranulation

Question 5

How does the bacteria stops the complement from acting?

Answer 5

Capsules of bacteria contain LPS that prevent triggering of the complement

Bacterial capsules have properties that allow for preferential binding of the wrong antibiotic

Some capsules bind the binding of C3b (part of alternative pathway) and some prevents C3b receptor access

Bacteria can sequester Factor H which usually controls the complement, so therefore negatively regulates the complement

Bacteria can secrete and destroy C5a (important molecule that promotes inflammation)

Question 6

How can the bacteria can prevent phagocytosis or survive the process?

Answer 6

If the bacteria contains leucocidins, this will kill the macrophages and prevents opsonisation

Some have capsules which are not recognised by phagocytes

Intracellular pathogens are hidden from serum killing, complement and antibodies and therefore surface within macrophages

• Resist oxidative killing
• Prepares cell for invasion
• Inhibit phagosome-lysosome fusion and escape going to cytoplasm

Question 7

What are the mechanisms that enable life inside macrophages?

Answer 7

Question 8

What happens if there is production of Fc receptors by microbes?

Answer 8

Leads to antibody inhibition

Question 9

How can adatpive immunity be evaded?

Answer 9

• the antigen can hide inside cells and block MHC antigen presentation
• immunosupression
• persistance/latency/reactivation
• Mutation of epitopes - If pathogens can modify their selves they can stay ahead of B cells and T cells

Question 10

How does step pneumoniae stop and tamper with immune responses?

Answer 10

Can cause pneumonia, meningitis and sepsis

Pathogenic mechanisms:

• Escapes phagocytosis
• Inflammation - lung damage
• Damage to endothelial cells
• By-passes defences controlled by surfactants

Question 11

What is antigenic variation?

Answer 11

= mechanisms that allow for pathogens to produce different types of antigens, or if they stay for a prolonged period of time in a population

• Phenotype changes - colony morphology, virulence, serotype, loose flagella
• Antigenic diversity/polymorphisms can produce genetically stable and alternative forms of antigens in a population of microbes
• Phase variation = ON/OFF of an antigen at low frequency occurs - during a course of infection in an individual host or during spread of microbe in community