Part 4

Question 1

How is a B cell or T cell receptor activated?

Answer 1

• Binding to antigen it recognizes, and the site that the B/T cell receptor binds to on the antigen is the epitope.

Question 2

What is two part process involved in the lymphocyte activation (activation of a B or T cell)

Answer 2

1. ) Clonal expansions and selection:
   - This is in response to signaling from the B cell or T cell receptor getting activated.
   - This response is a series of mitotic divisionary actions to get more of the appropriate B or T cell.
   - Its easier to think of it in terms of you know a specific kind of antigen is present, therefore your need more receptors for them to mount to.
   - ——————————————————————-
2. ) Undergo series of cellular changes necessary to fighting the infection.
   - B- Cells, this means prepare a bunch of antibodies (humoral response.)
   - T-cells, this means get ready to kill infected cells (humoral response.)

Question 3

Describe in depth the process of clonal expansion and selection, using the example of B-cells that reedy used. (same for both B and T cells btw)

Answer 3

1. ) A population of B cells lets say is hanging out in a lymph node. It is important to note that their receptors are unique to each B cell.
2. ) If one B-cell binds to an epitope that it can recognize then that causes in cross linking of B cell receptors ( two receptors heavy and light chains touch)
3. ) The cross linking causes a signaling cascade within the cell which results in series of rapid mitotic divisions .
4. ) which ultimately leads to a production of specific B-cells (with the correct receptor for the influx antigen population present)

Question 4

Describe in depth the process of cellular changes, using the example of B-cells that reedy used.

Answer 4

• the cellular changes result in manipulation of antibody production, (antibodies are a class of proteins)
• protein secretion involves proteins going through the endomembrane system (which includes the rough ER.
• therefore an active B cell has massive changes in the volume of its rough ER, it is way larger.

Question 5

Describe in depth the process of cellular changes, using the example of T-cells that reedy used.

Answer 5

• An activated T-cell would use chemical changes to assist in making the cell more mobile so it could move around and find toxic cells to destroy.

Question 6

Where and when does the process of lymphocyte activation occur at?

Answer 6

• It occurs in the peripheral lymphoid tissues (anything associated with the lymphatic system is a safe bet)
• following the DNA recombination event and following the clonal expansions and selection.

Question 7

How does a lymphocyte get activated?

Answer 7

Step 1: the B or T cell have to have a primary exposure to a respective antigen.
- in the case of B cells this is a direct exposure, meaning that B cells have to encounter antigens directly in some lymphatic tissue .
- T Cells don’t directly encounter antigens, but rather encounter phagocytic cells of the innate immune system. These phagocytic cells have ran into the antigen and used phagocytosis on it and are displaying pieces of it on their surface.
—————————————————————————
THIS PARITAL ACTIVATES THE B OR T CELL
—————————————————————————-
- Step 2: The B or Cytotoxic T cell have to receive a chemical signal, cytokine, from helper T cells that have encountered the exact same antigen.
- like a safety check, you don’t want lymphocytes to be activated inappropriately because then you’ll get an immune response when you don’t want one.

Question 8

What is the difference between MHC class 1 and MHC class 2?

Answer 8

• MHC class one is expressed on all cell types, and these are displaying random fragments of intracellular molecular molecules.
• EX; if you look at a liver cell that is randomly degrading pieces of what ever protein that is inside of it, and then displaying those proteins on its surface via the MHC 1 complex.
• This is how for example the activated cytotoxic T’s are able to identify a cell that has been infected, because an infected cell will not only display pieces of their own proteins but the pathogens as well.
• MHC 2: this is only expressed in phagocytic cells (dendritic cells, macrophages, neutrophils, and B-cells) and it serves to display fragments of materials that have been phagocytosed on the surface of the cell.

Question 9

What is the difference between MHC class 1 and MHC class 2?

Answer 9

• MHC class one is expressed on all cell types, and these are displaying random fragments of intracellular molecular molecules.
• EX; if you look at a liver cell that is randomly degrading pieces of what ever protein that is inside of it, and then displaying those proteins on its surface via the MHC 1 complex.
• This is how for example the activated cytotoxic T’s are able to identify a cell that has been infected, because an infected cell will not only display pieces of their own proteins but the pathogens as well.
• MHC 2: this is only expressed in phagocytic cells (dendritic cells, macrophages, neutrophils, and B-cells) and it serves to display fragments of materials that have been phagocytosed on the surface of the cells. These are being displayed to helper T cells or cytotoxic T cells

Question 10

Describe the example of MHC class 2 in dendritic cells that whats his nuts used?

Answer 10

• The dendritic cell encounters something in the environment (antigen) that doesn’t seem right and interacts with it. The dendritic cell phagocytoses it to get it in the cell.
• This then gets delivered to an endosome, which contains MHC class 2 proteins, following the antigen being degraded into smaller pieces, these pieces then bind to MHC class 2 proteins and get packed into vesicles.
• The vesicles then head to the cell surface. Once at the cell surface these dendritic cells display pieces of the antigen it encountered via MHC class 2.
  (innate immune system)
  ——————————————————————-
• These dendritic cells then travel through what ever means necessary to get to area where T cells can sense the antigen piece + MHC class 2 protein.
  ( adaptive immune system)

Question 11

What is a CD4+ cell vs a CD8+ cell?

Answer 11

• helper T cells specific proteins present on surface = CD4+ cell
• CD8+ cell = cytotoxic T cells specific proteins present on surface.

Question 12

Follow a dendritic cell being exposed to a potentially harmful antigen and using phagocytosis to bring it in the cell. Then putting it in an endosome so it can be degraded and vesiclelized with MHC class 2, and finally head to the surface of the dendritic cell. Last but not least, head to the area where T cells are located... What happens next?
( T-Cell activation)

Answer 12

• Here a helper T cell and a cytotoxic T cell with the version the the T-cell receptor that recognizes the antigen piece on the dendritic cell, then these bind.
• In the cytotoxic T cell it causes it to initiate the process of activation.
• But it also needs a signal from the helper T-cell to become fully activated.
• Then clonal expansion and selection, and the process of cellular changes necessary to get the cytotoxic t cell ready to function.
• When ready the cytotoxic T cells cruise the body looking for cells showing the same antigens in their surface so they can be destroyed.

Question 13

Describe B cell activation?

Answer 13

• B-cells are very good at phagocytosis, and they will cruise around looking for foreign material they can bind to, via their B cell receptor.
• ## They will then bring the antigen in via phagocytosis and degrade the antigen into pieces , then display those pieces via MHC class 2 on their own surface.partially activated at set point
  —————————————————————————-
• Then they begin to look for Helper T cells with the respective antigen receptor.
• If found, the helper T cells binds and secretes the cytokine to finish B cell activation…
• at which point you get Clonal expansion and selection as well as The process of cellular changes ultimately leading to the secretion of antibodies.