Cell mediated immunity

Question 1

Reminder of CD4 T cells

Answer 1

T cell = CD4+ = MHC2 = expressed on all nucleated cells in the body except RBC, platelets and nerves = EXogenous antigen processing = phagocytosis route

Question 2

Reminder CD8 T cells

Answer 2

T cell = CD8+ = MHC1 = surface of AP cells (dendritic, macrophage, b cells) = ENdogenous antigen processing = ER, Golgi etc

Question 3

3 types of T cell

Answer 3

• Cytotoxic CD8 T-cells
• T-helper 1 CD4 T-cells
• T-helper 2 CD4 T-cells

Question 4

What are the types of animal infection we are concerned with and what do they mean?

Answer 4

• Extracellular infection OR
• Intracellular infection?
This dictates how antigen is presented and therefore the type of immune response

Question 5

What are lymphocyte surface markers key for?

Answer 5

For lymphocyte subset function- slight differences in these surface markers dictate the subset of the T or B cells

Question 6

Talk through the process of T lymphocyte surface markers when presented with antigen.

Answer 6

1. T cell receptor on T lymphocyte (CD4 or CD8) accepts antigen from MHC (1 or 2) molecule.
2. MHC2 = CD4 and MHC1 = CD8.
3. CD 4/8 molecule BINDS to basal part MHC molecule, stabilising the interaction between TCR adn MHC antigen complex = strengthens signal between T cell and APC

Question 7

How do we sustain immune cells within a host?

Problems mean?

Answer 7

CD25 binding to interleukin 2 (IL-2) sustains immune cells.
Problems with IL-2 production will lead to the host being unable to sustain leukocyte populations.
Severe immunodeficiency dogs lack IL-2 production which leads to poor leukocyte production.

Question 8

How is the immune system further divided when lymphocytes encounter antigen?

Answer 8

B lymphocytes = antibody secreting B cells
T lymphocytes =
Cytotoxic T Lymphocytes (CD8/MHC I) and kill pathogens
Helper T cells (CD4/MHC II) that activate (cell-mediated) CTL cells AND stimulate (humoral) antibody production

Question 9

What is the difference in intracellular and extracellular infections?

Answer 9

Determined by site of infection….
Intracellular – Antibodies cannot function (not able to penetrate cell membrane) – need to kill infected cell – Cytotoxic T cells
Extracellular – Antibodies best defence – hence B cells secrete antibodies to bind pathogen

Question 10

What are cytokines?

Answer 10

• Soluble small protein messengers of the immune system.

Question 11

How do cytokines act?

Answer 11

Made by all cells – act in 3 ways:

1. autocrine (self) working on cell that produced it
2. paracrine (local cytokine microenvironment) cell that didn’t produce it but is neighbouring, within same lymphnode. On a cell that didn’t produce but neighbouring
3. endocrine - cytokines working on systemic level (long distance) usually only during large magnitude responses = cytokine storm/sepsis – large amounts of cytokines are a bad thing – downstream effects = inflammation, acting over entire system