Immunology 3 4 - Complement, T cell, etc

Question 1

4 methods for AB effector mechanisms

Answer 1

B cell receptor; Simple binding; Cell-surface binding via the Fc region: Opsonisation, NK cell ADCC and mast cell degranulation; Complement activation

Question 2

Describe B cell receptor AB mechanism

Answer 2

AB on surface of B cells act as antigen receptors, internalize antigen. Binding and cross-linking of the surface antibodies signal B cell, and internalized antigen is processed and presented to a helper T cell, which in turn further activates the antigen-presenting B cell.

Question 3

Describe the Simple Binding AB mechanism

Question 4

What are the types of Cell-surface binding via the Fc region? Describe the basics a bit

Answer 4

Some cell types have Fc receptors so they may bind ABs in solution. When the AB binds an antigen, the cell bound to the Fc region can react. (note: can have many different ABs on one cell). This includes mast cells and basophils; macrophages and granulocytes.

Question 5

Describe the mechanism of AB opsonization

Answer 5

AB binds to pathogen. Phagocytes come bind to it via Fc receptors, stabilizes and increases phagocytosis. (note: opsonization can also happen with complement parts, but this requires complement receptors)

Question 6

Describe ADCC

Answer 6

NK cells bind to Fc of ABs ALREADY bound to pathogen. Depends on avidity (overall strength) of interaction. Results in ADCC (AB dependent Cell-mediated Cytotoxicity)

Question 7

Describe Mast cell degranulation

Answer 7

Mast cells have high affinity for IgE, so they grab them out of solution, When the IgE bind antigen and cross link (ie two different ABs bind same antigen), the mast cell releases large amounts of histamine

Question 8

Describe the mechanism of compliment

Answer 8

Basically, when it is activated, some things bind to cells as opsonin and some float away and stimulate inflammation and chemotaxis. Some parts also lead to the membrane attack complex.

Question 9

Describe briefly the classical, alternate and lectin pathways

Answer 9

Classical is activated by AB/antigen complexes. Alternate constantly activated and covers host cells and pathogens, but host cells have regulatory proteins on surface to prevent its action. Lectin: binding of microbe polysacc to circulating lectins. Lectins are structurally similar to Clq, so it triggers complement system. No AB, rest of pathway is same as classical

Question 10

What is cleaved when C3, C4, etc split?

Answer 10

Cleaves a thioester bond, then it can bind to something else. C3b binds to cell, other factors, then activates.

Question 11

Compare the different AB and their relative function with complement

Answer 11

Picture

Question 12

T cell receptor TCR

Answer 12

Like an AB but only one binding site. One light and one heavy chain. Specific for the antigen peptide and the MHC protein

Question 13

CD3

Answer 13

Necessary for TCR to work, and always associated with it. It is made of gamma, delta and epsilon chains (one each). CD3 is responsible for signalling inside the T cell.

Question 14

T cell maturation (early)

Answer 14

Develop receptors, then go through self/non-self selection

Question 15

Pairs which stabilize interaction for initial activation of naive T cell (signal and co-signals)

Answer 15

Listed T cell protein then target or APC. TCR/MHCI + peptide; CD8/MHCI; CD4/MHCII; CD28/B7; CD2/LFA-3; LFA-1/ICAM-1; CD40L/CD40 (APC only)

Question 16

What happens when naive T cell is triggered?

Answer 16

Release IL-2 autocrine, then become several cell types: Th for AB production, Th for delayed type hypersensitivity (for activating macrophages), Th for allergic/parasitic response, Th for T cytotoxic response, Tc cells, and memory T cells

Question 17

What happens inside T cell when activated?

Answer 17

Cascade of signals, lots of phosphorylation leading to transcription for cytokines etc

Question 18

Cyclosporin A and FK504

Answer 18

Immunosuppressive drug which targets calcineurin which is a phosphatase in the T cell. Blocking it stops the T cell from activating. FK504 is something similar.

Question 19

How is naive Th cell activated

Answer 19

First get activated in lymph node when interact with dendritic cell and start to differentiate, but require another stimulus from MHC class II expressing APCs, including dendritic cells, macrophages, or B cells

Question 20

Mutual stimulation b/w Th cell and B cell?

Answer 20

B cell ingests and displays antigen, matching Th cell binds via TCR/CD3 (Th signal 1), CD28/B7 (Th signal 2), then Th cell produces more CD40L to stimulate B cell more. B cell makes cytokine receptors, which can influence class switching and affinity maturation

Question 21

Affinity maturation of B cell

Answer 21

Proliferates, generating mutations in variable regions of AB. Weak affinity die, good ones continue and dominate the response. Memory cells persist after

Question 22

B cell memory

Answer 22

There are more B cells specific to that antigen, they are the more specific ones, and the class switch has already occurred. All of these contribute to more effective response next time.

Question 23

T dependent vs independent response

Answer 23

T dep requires B cell to interact w/ Th cell to get going. T indepe. B cell just binds to a polysaccharide or something like that, No class switching or affinity maturation. Insert pic