B & T cell activation, and development, cytokines, mhc 1

Question 1

B cells are the leukocytes that turn into?

Answer 1

Plasma cells and release antibodies once they have been activated.
- Antibody is the most important part of the humoral immune system, it is a secreted free floating form of the BCR so whatever antigen activated the B cell through an interaction with the B cell receptor will also be recognized by the antibody

Question 2

B cells are activated when?

Answer 2

Primarily in response to extracellular pathogens (most bacteria)

Question 3

Two main types of T cells each part of the cell mediated immunity

Answer 3

1) CD4+ helper: Don’t fight pathogens directly but help various other cells to do so my releasing cytokine signals.
- There are two subtypes of CD4+ Helper cells
* Th1- primarily activates cytotoxic CD8 T cells and macrophages
* Th2- primarily activates B cells
2) CD8+ cytotoxic: Release porforin and granzyme to cause lysis of the infected cells. These cause apoptosis of cells that are infected by intracellular pathogens such as viruses & small number of intracellular bacteria such as chlamydia or ligonella. Also play a role in triggering apoptosis of cancerous cells to prevent the spread of cancer

Question 4

Describe the extracellular pathogens pathway

Answer 4

1) Antigen present on extracellular pathogen will bind to the B cell receptor (BCR) and can go in one of two ways

Question 5

B & T cell development

Answer 5

• Arise from stem cells in bone marrow
• Immature B cells remain in the bone marrow to complete maturation
• Immature T cells leave the bone marrow & travel to the thymus to complete maturation
• Bone marrow & thymus are referred to as primary lymphoid organs, this is where B cells and T cells differentiate & mature

Question 6

What happens in the absence of primary lymphoid organs?

Answer 6

Prevents the normal development of WBCs & can lead to immunodefeciency

Question 7

What happens once B & T cells mature?

Answer 7

They move to the secondary lymphoid organs such as the lymph node & spleen. This is where the cells come into contact with the foreign particles.

• If the pathogen that the cell can interact with the cell will be activated, after activation the cell proliferates making clones of itself that are all capable of recognizing & fighting against the same antigen (pathogen)
• However not all T & B cells will be activated, a large majority of the mature cells will not encounter the type of foreign material they recognize. If the pathogen or foreign material that the B or T cell can fight against isn’t present in the body there is no need to be activated
• The foreign material or pathogen that the cells recognize is determined by the unique surface receptors on those cells

Question 8

An antigen is the specific structural sequence the receptors can bind to. All of the receptors on a given T or B cell are the same & recognize the same antigen. When the receptor binds to the appropriate antigen what happens?

Answer 8

It signals the cell to become active & proliferate

Question 9

What are the Major Histocompatibility Complexes (MHC)

Answer 9

• They are the cells surface molecules encoded by the human leukocyte antigen genes (HLA) genes
• MHC’s present antigens to T-cell receptors
• T-cell receptors cannot recognize antigen without MHC
  
  • The MHC is like a cup that holds whatever antigen in it, and the T cell won’t recognize the antigen in the cup unless the cup is also there
• With CD4 & CD8 cells the antigen presented must be a protein (peptide)

Question 10

MHC1

Answer 10

• Present on all nucleated cells means its on every cell thats not a red blood cell
• Activates CD8

Question 11

MCH2

Answer 11

• Activates CD4

Question 12

How are CD4 T-cells activated?

Answer 12

By an interaction with the antigen presenting cells (APS)
- The APS usually macrophages or dendritic cells phagocytose extracellular pathogens, break them up into tiny fragments, then present those fragments on their surface MHC II so that the MHC II & the antigen can interact with the CD4 T cells & activate those CD4 cells

Question 13

How are CD8 cells activated?

Answer 13

By an interaction with the cell that has an intracellular infection

• The antigen is presented on the surface MHC I of infected cell
• To become active the CD8 cell must recognize the antigen and the MHC

Question 14

B cells can be activated in two ways, one being T-cell dependent, explain this process

Answer 14

B-cell activation
An interaction between Th2 helper cells is required to activate the B cell. The B cell presents the antigen, it attracts a T-cell to come over, once the binding between the two cells happens, the T cell is activated. Once the Helper T cell is activated, it releases cytokines and in turn activates that B-cell, B-cell goes on to then create antibodies

Question 15

Interleukin 1 (IL-1)

Answer 15

Released by macrophages during acute inflammation to cause a change in the vessel endothelium that promotes neutrophil extravasion, also plays a role in formation of fever

Question 16

Interleukin 2 (IL-2)

Answer 16

Secreted by T cells to stimulate proliferation of other T cells.
Some immunosuppressants inhibit IL-2 production in order to

Question 17

Released by T-cells & NK cells in response to intracellular infections like viruses or TB. Activates macrophage phagocytic activity & causes infected cells to inhibit virus protein synthesis.

Answer 17

Interferon (IFN)

Also plays a key role in activating macrophages to form granulomas

Question 18

Mediates septic shock as well as increasing apoptosis of cancer cells

Answer 18

Tumor necrosis factor