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Biology 4.1 Immunity (T cells and B cells)

Hi all! I’m hoping that someone can help me, as I am really confused as to how T and B lymphocytes work, as in my brain different videos that I am seeing are conflicting! It seems that some say that T lymphocytes only attach to antigen presenting CELLS, whether that be a cancer cell, macrophage that has engulfed a pathogen, an infected cell, or a transplanted cell. These T lymphocytes upon attaching to the correct antigen become ‘activated’ and so release a type of cytokine called interleukins, which trigger the mitosis of T lymphocytes and B lymphocytes, which then differentiate into their different types. These interleukins also stimulate the macrophages so more phagocytosis occurs. That all makes sense to me, but what I don’t understand is this:

Then it suggests that this activated T lymphocyte (is the original T lymphocyte a T helper cell? If not how does this work?) attaches to a B lymphocyte which has become an antigen presenting cell by engulfing the pathogen. Then the interleukins released stimulate the B lymphocyte as well as the other aforementioned cells. I don’t understand why this occurs, as this surely isn’t necessary because the interleukins have already been released, and the activated T cell has already come across an APC. Can someone help me to understand what is going on here? Thank you :smile:
I forgot to say that this is A Level Biology OCR A
Reply 2
Original post by raindropxox
Hi all! I’m hoping that someone can help me, as I am really confused as to how T and B lymphocytes work, as in my brain different videos that I am seeing are conflicting! It seems that some say that T lymphocytes only attach to antigen presenting CELLS, whether that be a cancer cell, macrophage that has engulfed a pathogen, an infected cell, or a transplanted cell. These T lymphocytes upon attaching to the correct antigen become ‘activated’ and so release a type of cytokine called interleukins, which trigger the mitosis of T lymphocytes and B lymphocytes, which then differentiate into their different types. These interleukins also stimulate the macrophages so more phagocytosis occurs. That all makes sense to me, but what I don’t understand is this:
Then it suggests that this activated T lymphocyte (is the original T lymphocyte a T helper cell? If not how does this work?) attaches to a B lymphocyte which has become an antigen presenting cell by engulfing the pathogen. Then the interleukins released stimulate the B lymphocyte as well as the other aforementioned cells. I don’t understand why this occurs, as this surely isn’t necessary because the interleukins have already been released, and the activated T cell has already come across an APC. Can someone help me to understand what is going on here? Thank you :smile:

T-cell activation requires both binding of the T cell to antigens on the surface of antigen presenting cells AND cytokines. The cytokines released influences T-cell differentiation i.e what type of T-cell it will become (there are many types of helper T cells). Activated T-cells will produce cytokines, however, this is not enough to activate B-cells.

B-cell activation is also very complicated. For the most part, B cells require T-cells to become activated, however, sometimes B-cells can be activated without help from T-cells (T-cell independent activation). This is determined by the type of antigen. B-cells present antigens on their surface just like professional APCs. Activated T-helper cells bind to this and activate the B-cells, causing them to proliferate and differentiate into plasma cells which produce antibodies and memory B-cells.
Original post by Jpw1097
T-cell activation requires both binding of the T cell to antigens on the surface of antigen presenting cells AND cytokines. The cytokines released influences T-cell differentiation i.e what type of T-cell it will become (there are many types of helper T cells). Activated T-cells will produce cytokines, however, this is not enough to activate B-cells.
B-cell activation is also very complicated. For the most part, B cells require T-cells to become activated, however, sometimes B-cells can be activated without help from T-cells (T-cell independent activation). This is determined by the type of antigen. B-cells present antigens on their surface just like professional APCs. Activated T-helper cells bind to this and activate the B-cells, causing them to proliferate and differentiate into plasma cells which produce antibodies and memory B-cells.


Thank you!! That helps me to make sense of all the information I have found! Just one thing, with the T cell activation, where do these cytokines come from? (The cytokines that activate the T cells) thank you :smile:
Reply 4
Original post by raindropxox
Thank you!! That helps me to make sense of all the information I have found! Just one thing, with the T cell activation, where do these cytokines come from? (The cytokines that activate the T cells) thank you :smile:

Antigen presenting cells also release cytokines.
Original post by raindropxox
Hi all! I’m hoping that someone can help me, as I am really confused as to how T and B lymphocytes work, as in my brain different videos that I am seeing are conflicting! It seems that some say that T lymphocytes only attach to antigen presenting CELLS, whether that be a cancer cell, macrophage that has engulfed a pathogen, an infected cell, or a transplanted cell. These T lymphocytes upon attaching to the correct antigen become ‘activated’ and so release a type of cytokine called interleukins, which trigger the mitosis of T lymphocytes and B lymphocytes, which then differentiate into their different types. These interleukins also stimulate the macrophages so more phagocytosis occurs. That all makes sense to me, but what I don’t understand is this:
Then it suggests that this activated T lymphocyte (is the original T lymphocyte a T helper cell? If not how does this work?) attaches to a B lymphocyte which has become an antigen presenting cell by engulfing the pathogen. Then the interleukins released stimulate the B lymphocyte as well as the other aforementioned cells. I don’t understand why this occurs, as this surely isn’t necessary because the interleukins have already been released, and the activated T cell has already come across an APC. Can someone help me to understand what is going on here? Thank you :smile:
When revising with daughter when she did her alevels there was a video by BioRach and she explained it pretty good. It is OCR, but i would think the facts will be the same where ever exam board it is. I posted what i know so i think i got them all?
Cell mediated immunity
immune response overview
Humoral immunity with interleukins

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