Unit 7: Parasite Infections

Question 1

what makes parasites living in the skin (such as bot fly larvae) successful?

Answer 1

it is an area of low immune surveillance and they only persist for a short amount of time

Question 2

what does the blood brain barrier reduce/prevent?

Answer 2

trafficking of some immune cells, prevents antibodies reaching the brain

Question 3

how do antibodies kill/affect/interact with parasites?

Answer 3

• neutralization of essential antigens
• activation of MAC complement cascade (lyse targets and C3b)
• act as opsonin’s

Question 4

What expresses IgG?

Answer 4

phagocytes (neutrophils, macrophages)
isotypes have different properties

Question 5

What expresses IgE?

Answer 5

eosinophils, basophils, mast cells (absorbed onto cells before interaction with antigen)

Question 6

how is IgM produced?

Answer 6

by naive B cells on first contact
followed by: helper T cell (CD4) bind MHC II (cytokine production) -> memory cells + plasma cells (IgG, IgA, IgE)

Question 7

What is different about IgA?

Answer 7

only found on mucosal surfaces, eg, is normally secreted into the intestines

Question 8

what is steric interference? give an example

Answer 8

natural antibodies block neutralising antibodies
plasmodium infection natural antibodies can stop monocloncal antibodies which are designed to block erythrocyte invasion -> eg, IgM bigger molecule than the more ‘effective’ IgG

Question 9

what factors control antibody production?

Answer 9

T cell cytokines -> Th1/2

Question 10

examples of Th2 responses

Answer 10

increase production of IL-3-6,10
help B cells produce antibodies via proliferation and isotype switching
IL-5 = IgE production

Question 11

examples of Th1 responses

Answer 11

increase production of TNF and gamma interferon
help cell-mediated immune responses via macrophage and cytotoxic T cell recruitment

Question 12

name the stage specific antigen seen on sporozoites

Answer 12

circumsporozoite protein (CSP) - not seen in blood or sexual stages

Question 13

mechanism behind ‘smokescreen’ effect in eg, trypanosomes

Answer 13

VSG released from surface by phospholipase C (antibody binding action)
soluble VSG competes with VSG = antibody incapacitation

Question 14

how do antigens with repeating epitopes affect host immune response?

Answer 14

cross-linkage on B cell surface receptor = B cell proliferation + IgM expression = less effective clearance
resistance to T cell signals that cause isotype switching/ affinity maturation

Question 15

What is effective at clearing extracellular parasites?

Answer 15

IgE
BUT
can coat exterior with glycans, stimulate Th1 response or non-specific IgE absorption onto FcE (cross-linkage interference)

Question 16

advantages of hiding in erythrocytes?

Answer 16

no nucleus - limited invasion response
no intracellular killing mechanisms
don’t express MHC I (cant present antigen)

Question 17

how do macrophages kill intracellular parasites?

Answer 17

PRRs
phagocytosis
anti-microbial peptides
lysosomal enzymes

Question 18

different Th responses?

Answer 18

IL-12 production (macrophage) = naive T cell develop into Th1
Th1 = activation of phagocytosis
(Th2 doesn’t help clear intracellular)

Question 19

how does leishmania modify Th responses?

Answer 19

selective inhibition of IL-12 = reduction of Th1 production
stimulation of IL-10 production = reduce MHC II, increase Th2 cell = suppression of macrophage function