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

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Flashcards in B & T cell activation, and development, cytokines, mhc 1 Deck (18):

B cells are the leukocytes that turn into?

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


B cells are activated when?

Primarily in response to extracellular pathogens (most bacteria)


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

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


Describe the extracellular pathogens pathway

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


B & T cell development

- 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


What happens in the absence of primary lymphoid organs?

Prevents the normal development of WBCs & can lead to immunodefeciency


What happens once B & T cells mature?

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


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?

It signals the cell to become active & proliferate


What are the Major Histocompatibility Complexes (MHC)

- 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)



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



- Activates CD4


How are CD4 T-cells activated?

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


How are CD8 cells activated?

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


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

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


Interleukin 1 (IL-1)

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


Interleukin 2 (IL-2)

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


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.

Interferon (IFN)
Also plays a key role in activating macrophages to form granulomas


Mediates septic shock as well as increasing apoptosis of cancer cells

Tumor necrosis factor