Immunology Processes

Question 1

How are B cells made and where are they activated?

Answer 1

Hematopoietic stem cells in the bone marrow differentiate into a pro B cell, then a large pre B cell, then a small pre B cell, and then an IgM B cell, forming the BCR via VDJ recombination
-these migrate through the blood to secondary lymphoid organs to be activated

Question 2

How are B cells activated?

Answer 2

Foreign antigens bind the BCR on the B cell. The B cells present this on MCHII to a helper T cell. It receives co-stimulation like CD40 and cytokines from the helper T cell. This causes the B cell to proliferate and promotes the formation of germinal centers and long-lived plasma and memory B cells. The type of cytokine determines antibody type

Question 3

What is the immune response in the lymph nodes?

Answer 3

• Antigen and APC from tissue travels into lymph node through afferent lymphatic channels.
• Antigens processed by resident dendritic cells in the paracortex
• Resident dendritic cells present antigen on MCHII to CD4 T helper cells, activating them
• B cells activated by T helper cell or antigen directly
• Activated B and T cells form primary follicles, which leads to the production of secondary follicles with germinal centres
• Plasma B cells secrete antibodies which leave through efferent lymphatic vessels

Question 4

What is the immune response in the spleen?

Answer 4

• Foreign antigens are carried to the spleen from the splenic artery
• Dendritic cells captures the antigens in the marginal zone, and move to the PALS along with T cells from the splenic artery
• In the PALS dendritic cells activate helper T cells
• Active helper T cells activate B cells which form secondary follicles with a germinal centre

Question 5

How are long-lived plasma B cells or memory B cells formed?

Answer 5

• A naive B cell moves into the dark zone of a germinal centre
• In the dark zone it recieves costimulatory signal from CD4 helper T cells, causing them to undergo proliferation and somatic hypermutation
• They are then selected for survival in the light zone. B cells with unfavourable BCR mutations are killed by apoptosis. B cells with favourable BCR mutations move further into the light zone
• Here they receive a second survival signal from T helper cells and differentiate into either plasma or memory B cells

Question 6

How are T cells activated and how are memory T cells produced?

Answer 6

• Naive T cell is activated by a dendritic cell that presents an antigen to it
• Naive T cells then differentiate into effector cells
• Most effector T cells die by apoptosis after a few days, but some recieve survival signals from cytokines like IL-7 and/or IL-15
• Forms a central memory T cell that has CCR7 and remain in lymphoid tissue
• Forms an effector memory T cell that dosent have CCR7 and lives in tissues

Question 7

What is the immune response in the gut?

Answer 7

• The gut contains peyer’s patches which contain a pocket of clusters of B cells, T cells, dendritic cells, macrophages and germinal centres
• An antigen is sampled and transported into the pocket by microfold cells using transcytosis
• The antigen is taken up by dendritic cells, which then leads to the activation of T and B cells in the lamina propria

Question 8

How do cytotoxic T cells become activated and exert its function on a virus?

Answer 8

• Infected cells present present viral antigens on MHCI
• Infected cells upregulate the fas receptor on its surface
• Dendritic cells present viral antigens on MCHI via cross presentation
• Cytotoxic T cell binds via its TCR and CD8 coreceptor and become activated
• Fas ligand on cytotoxic T cell is upregulated and binds to fas on the infected cell triggering apoptosis of the infected cell
• The cytotoxic T cell releases perforin and granzyme to trigger apoptosis of the infected cell