- Sorry that first part was just a mistake
- I am sort of confused at what you are saying so do th cells proliferate at all and how do they do it?
- So after a Th binds to the MHC 11 of an APC, what happens because now i am so confused
Sorry, didn't mean to confuse you. Basically when a cell becomes viral infected both cell mediated and humoral immunity are activated. I'll go over everything tell me if something doesn't make sense.
General process always occurring in our bodies:
-B cells mature in the bone marrow. Here they are tested for self-reactivity, if they can bind to a self antigen they are normally destroyed (except for malfunctions ie autoimmune diseases.)
-Both Tc cells and Th cells mature in the thymus gland. Here they are also tested for self reactivity.
Throughout the body there are always B cells, Th cells, and Tc cells with a randomly generated antigen specificity.
B cells are found in lymph nodes (and throughout the lymph system)
Th cells are found in lymph nodes
Tc cells are found throughout the body tissues.
Normally:
B cells and Th cells just hang about waiting for their antigen to bind/be presented to them.
Tc cells travel throughout the body attempting to bind to peptide fragments presented on MHC1 markers.
If an intracellular pathogen (ie virus) enters the body, parts of it will inevitably end up in the blood and lymph. Some of it will enter cells and cause the creation of non-self peptide fragments which will be presented on MHC 1 markers at some point. The following will happen
simultaneously. Humoral Immunity will be activated:
-A naive B cell will bind to a free antigen (ie. not presented by an APC).
-A Th cell will be presented with its antigen on a MHC2 molecule by an APC.
-The 'selected' B cell and Th cell will then find each other and if they have bound the same antigen, the Th cell will release cytokines (the same cytokines that affect cell mediated immunity - see below.)
-These cytokines cause the B cell to divide (proliferate) and differentiate into B memory cells and B plasma cells.
-These cytokines also cause the Th cell to divide (proliferate) and differentiate into Th memory cells and Th active cells.
-The memory cells remain in the body to fight subsequent infection by a pathogen with the same antigen specificity and the B plasma and Th active cells fight off the current infection.
As the pathogen (virus) is intracellular, cell mediated immunity is also activated.
-Naive Tc cells are always travelling throughout the body, attempting to bind to peptide fragments presented on MHC1 markers.
-When they find one that they can bind to, the Tc cell is 'selected'.
-The Tc cell will release granzymes (including perforin) which causes the cell to undergo apoptosis.
-The Tc cell continues to travel throughout the body and kill cells presenting the same peptide but it will not divide and differentiate until cytokines are present.
-When cytokines have been released from Th cells (this could happen before or after the Tc cell is selected) the Tc cell will divide (proliferate) and differentiate into Tc memory cells and Tc active cells.
-The Tc memory cells will remain in the body to fight off subsequent infection by the same pathogen.
-The active Tc cells will travel throughout the body, inducing apoptosis in cells presenting the same peptide fragment.