Lecture 4

Question 1

What disease is caused by T. cruzi?

Answer 1

Chagas disease

Question 2

Apart from the triatomine bug, what other ways can T. cruzi be transmissed?

Answer 2

Trans-placentally - via C1q as a molecular bridge

Oral transmission - fecal contamination of food substances/accidnetal ingestion of reduviid bugs

Question 3

What was interesting about the oral transmission route?

Answer 3

Patients began to develop symptoms very quickly, rather then after 40 years as seen in triatomine vector infections

Question 4

What could have been causing the quick development of symptoms?

Answer 4

1) Differences in pathogenicity in different T. cruzi strains
2) Differences in oral pathogenicity
3) Differences in host-parasite interactions
4) More controlled study group
5) Earlier stage of the disease

Question 5

How does genetic variability of T. cruzi arise?

Answer 5

1) Clonal evolution

2) Genetic exchange between parasites

Question 6

How many discrete typing units of T. cruzi exist?

Answer 6

6
DTU are sets of stocks that are genetically more related to each other than to any other stick and that are identifiable by common genetic, molecular or immunological markers

Question 7

Describe the trypomastigote

Answer 7

Kinetoplast at the posterior, flagellum emerges posteriorly and folds back along body; attached to body as undulating membrane (um) with free flagella at anterior.

Question 8

Describe the epimastigote

Answer 8

Kinetoplast central, just anterior to the nucleus, flagella emerges from the middle with short (um), are more motile than the trypomastigotes

Question 9

Describe the metacyclic trypomastigote

Answer 9

Infectious form of the trypomastigote

Question 10

Describe the amastigote

Answer 10

Intracellular, cytoplasmic, more spherical, no free flagella (but has basal body and flagella base), kinetoplast near the nucleus and non-motile

Question 11

What happens during amastigotogenesis

Answer 11

From trypomastigote to amastigote
Takes place without nuclear division, asymmetric - one daughter with short flagella has nucleus and lives, one with long flagella dies

Question 12

What happens during cell division of an infected cell?

Answer 12

The amastigotes will commonly move to make sure both daughters are infected

Question 13

How do the parasites synchronise differentiation from amastigotes?

Answer 13

Know that the amastigotes have a finite number of divisions but what the cues are is unknown

Question 14

What percentage of the T.cruzi genome encodes surface proteins?

Answer 14

~50%

• gp63 surface proteases
• gp85/trans-sialidase superfamily
• mucins
• mucin associated surface proteins

Question 15

What is the role of gp72?

Answer 15

Attachment of the flagellum to the cell body of epimastigotes

Question 16

What role does the trans-sialidase play?

Answer 16

As T. cruzi cannot synthesis sialic acid, requires trans-sialidase to take it fomr host. Then used sialic acid for host cell attachment, invasion of the cytosol and host mimicry

Question 17

What role do the mucins play?

Answer 17

Involved in invasion and adhesion with the trans-sialidases

Question 18

What do the interactions between T. cruzi and mammalians cells drive?

Answer 18

• Phagocytosis
• Membrane raft-dependent endocytosis
• Macropinocytosis
• Autophagy
• Ca2+ dependent lysosome exocytosis

Question 19

Why does T. cruzi have many entry routes into the cell?

Answer 19

To allow promiscuity; and invade many types of cell

Question 20

What process is generally important for entry into non-phagocytic cells?

Answer 20

Induced lysosome exocytosis

Question 21

Outline induced lysosome exocytosis

Answer 21

Gp82 on parasite induces activation off DAG and IP3, leading to calcium mobilization from the ER, also involving PI3K and MTOR. Calcium dependent lysosomal trafficking to the plasma membrane occurs; actin and microtubule dependent.

Question 22

What must T. cruzi do no matter which entry route it used?

Answer 22

Escape from the vacuole

Question 23

Outline T. cruzi escape from the vacuole

Answer 23

After phagolysosome is established T. cruzi has a protein, TC-TOX, which is activated by the low pH and acts to create a pore in the membrane (similar to mammalian complement C9). T. cruzi uses its trans-sialidases to remove the sialic acid from the LAMPS which are trying to protect the membrane, allowing access by TC-TOX.

Question 24

What type of CD4+ T cells mainly involved in this infection?

Answer 24

Th1

Question 25

What roles do antibodies play?

Answer 25

• Antibody-dependent cell-mediated cytotoxicity for host protection
• Antibody-dependent cell-mediated cytotoxicity that is pathology inducing
• Lytic antibodies targeting trypomastigotes galactosyl residues
• Function blocking antibodies targeting parasite complement regulatory protein, e.g. decay accelerating factor (DAF)

Question 26

What type of T cells important in T. cruzi?

Why?

Answer 26

CD8
Antigens presented using MHC class I as the T. cruzi is in the cytosol

Question 27

What happens to the CD8 T cells in chronic infection ?

Answer 27

• Reduced effector function

- Loss of “stem-ness” in memory CD8 T cells

Question 28

How does the T. cruzi evade the immune response?

Answer 28

• Temporal escape
• Trans-sialidase on T. cruzi, adds sialic acid onto T cell so it cannot react on targets
• Have many variants of trans-sialidase to act as “smokescreen”
• Reproduction rate too fast, reproduced, burst out and infected new cells before immune response reaches them

Question 29

How has resistance to T. cruzi been enhanced?

Answer 29

Immune re-direction
Target the flagella of daughter cell of trypomastigote that dies rather than the trans-sialidases as there are few variants and give vaccine form to mice = enhanced resistance to T. cruzi