15 Immune defences in action

Question 1

Broadly speaking, antibodies are particularly important against extracellular infections, and T cell immunity more important for intracellular pathogens

What antimicrobial peptides does the skin produce for protection?

Answer 1

beta-defensins

cathelicidins

myeloperoxidase

lysozyme

Question 2

Patient with meningococcal/ gonococcal infection.

What is possible immune deficiency?

Answer 2

complement deficiency

Question 3

CRP is a pentameric beta globulin, produced by liver during inflammatory reactions, due to interleukin response (IL-6).

What is its role?

Answer 3

Reacts with phsophorylchlorine in bacteria cell wall, which activates complement and phagocytosis (opsonin)

Other acute phase proteins have similar effects

Question 4

Which interleukins are most important in producing fever?

Answer 4

IL-1

IL-6

Question 5

What is role of NK cells?

Answer 5

rapid, non-specific means of controlling viral/ intracellular infections

early source of cytokines/ chemokines including IFN-gamma, TNF-alpha

lyses infected cells with cytotoxic granules/ perforin

Question 6

Phagocytes can kill pathogens via oxidative and non-oxidative mechanisms

What is mechanism of oxidative killing?

Answer 6

Respirationg in phagocyte (anaerobic or aerobic) uses burst of oxygen consumption, which generates reactive oxygen intermediates such as superoxide ion, hydrogen peroxide and free hydroxyl radicals.

These are all toxic to microbe - either damage cell membrane, damage proteins, or altering pH of organism

Patients with chronic granulomatous disease have errors in this metabolism pathway, so cannot phagocytose/ kill pathogens

Bacteria which produce catalase can negate the effect of certain oxidative species

Question 7

Phagocytes can kill pathogens via oxidative and non-oxidative mechanisms

What is mechanism of non-oxidative killing?

Answer 7

oxygen not always available e.g anaerobic organisms

Phagocytic cells must use cytotoxic granules

Question 8

IFN alpha/ beta/ gamma all reduce viral replication in infected cells.

alpha/ beta produced by most cells
gamma produced by T cells

How do they do this?

Answer 8

Virally infected cell produces IFN, which binds to neighbouring uninfected cells

Uninfected cells produce protein kinase and 2’5’-oligoadenylate synthetase enzymes, which results in inhibition of viral RNA translation and protein synthesis