Lecture 5 Antigen presenting cells

Question 1

Where are macrophages made and the structure of macrophage

Answer 1

Most macrophages are made in the bone marrow

Macrophages have golgi, mitochondria, rounded nucleus, free ribosomes and rough endoplasmic reticulum

Question 2

Where are macrophages distributed and what are they called in these places? (5)

Answer 2

Microglia in brain
Kupffer cells in liver
Histiocytes in connective tissue
Monocytes in blood
Alveolar macrophages in lungs

Question 3

What are the 5 macrophage receptors

Answer 3

Transport receptors
Cytokine receptors
Complement receptors
Antibody receptors
Other receptors

Question 4

What are the 5 main functions of macrophages

Answer 4

Phagocytosis (slower than neutrophils but can kill bigger)
Apoptosis - removal of dead cells
Produce different cytokines - facilitate further development of innate and adaptive immunity
Trigger tissue repair and wound healing
Antigen presentation

Question 5

Describe the two types of Macrophages

Answer 5

M1 cells aggressively phagocytic
M2 cells trigger wound repair and healing
Can interchange

Question 6

How do macrophages know when to kill dead cells (apoptosis)

Answer 6

Macrophages send chemical signals out to neutrophils and if they dont respond back to macrophages with same signal the macrophages kill them

Question 7

Describe macrophage granuloma formation

Answer 7

If foreign material cant be removed/killed, M2 macrophages gather around it in large numbers and fibroplasts make a wall to prevent spread

Question 8

Describe dendritic cells and the what are the 4 subpopulations of dendritic cells (DCs)

Answer 8

Most important APC. Have long dendrites that enable them to trap antigens
Plasmacytoid DCs
Myeloid/classical DCs
Follicular DCs
Langerhans DCs

Question 9

Describe Classical DCs

Answer 9

Derived from macrophages
Classical DC 1s trigger type 1 responses
Classical DC 2s trigger type 2 responses and Th17 responses

Question 10

Describe follicular dendritic cells

Answer 10

In lymph nodes and spleen
present antigen to antibody producing B cells
Trigger somatic mutation (b cells mutate to generate improved antibodies)

Question 11

Describe Langerhan cells

Answer 11

In the skin

Traps antigens through epidermis

Question 12

Describe difference between immature and mature DCs

Answer 12

Immature DCs capture antigens and process them

Mature DCs present antigens to T and B cells

Question 13

Where do all APCS (Dendritic cells, B cells and macrophages) present their antigens to?

Answer 13

T helper cells

Question 14

Describe the Uptake of antigen by macrophages and presentation to T helper cells (extracellular)

Answer 14

The immunogen (antigen) enters the macrophages endosome and the endosome and lysosome fuse in the macrophage. Its here where the antigen is fragmented and the fragment binds to MHC II molecule and the MHC epitope molecule is transported to the surface of the macrophage were it can interact with the specific TCR on T helper cell.

Question 15

How is the T helper cell activated

Answer 15

The T helper cell requires 2 signals to become activated.
One signal is the binding of TCR to class II MHC molecule on APC
Other signal is provided by cytokines (chemotaxis) secreted by APC.

Question 16

Describe endogenous antigen processing

Answer 16

Virus enters the cell and forms a viral protein from its viral nucleic acid. The viral protein is ubiquninated is then fragmented by proteosome. The fragments then bind to MHC I molecules in cell and then transport on surface of cell. Recognised by and trigger responses in cytotoxic T cells

Question 17

Describe the role of T cells (Th and Tc)

Answer 17

APCs present Ag on MHC class II molecules to TCR on T helper cells
Presentation to a TH2 cell results in cytokine production that promotes Ab production
Presentation to a TH1 cell results in cytokine production that promotes CMI responses
Almost all nucleated cells can present Ag on MHC class I molecules to TCR of cytotoxic cells

Question 18

Describe the activation of B cells

Answer 18

B cells BCR binds to the specific MHC II antigen complex on a T H cell (already activated) The B cell can then proliferate into a memory B cell for future reference or differentiate into a plasma cell which will make antibodies for the antigen.

Question 19

Describe difference between T helper 1 cells and T helper 2 cells

Answer 19

T helper 2 cells after being bound to APC activate and secrete cytokines to initiate antibody production from B cells (humoral)
T helper 1 cells after being bound to APC activate and initiate CMI response (CMI)

Question 20

What is IL-2 and BCGF/BCDF

Answer 20

IL-2 released by Th cells to activate Tc cells
BCGF - B cell growth factor
BCDF - B cell differentiation factor
Th cells secrete BCGF and BCDF depending on if B cells want to proliferate (memory cells) or differentiate (plasma cells then antibodies)