DoubleDoors
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I do OCR AS Biology A, and I find that the textbook's interpretation of the stages of specific immunity (as far as I understand - phagocytosis->APC then the involvement of b and t lymphocytes) isn't great, and the revision guide seems to lack detail.

Does anyone have a good explanation to help me understand cell mediated and humoral immunity and their interdependence, as well as the production/roles of cytokines etc. (see specification below)

This is the segment of the specification that I would like some useful information on:
Image

Any help is greatly appreciated.
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AortaStudyMore
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(Original post by DoubleDoors)
I do OCR AS Biology A, and I find that the textbook's interpretation of the stages of specific immunity (as far as I understand - phagocytosis->APC then the involvement of b and t lymphocytes) isn't great, and the revision guide seems to lack detail.

Does anyone have a good explanation to help me understand cell mediated and humoral immunity and their interdependence, as well as the production/roles of cytokines etc. (see specification below)

This is the segment of the specification that I would like some useful information on:
Image

Any help is greatly appreciated.
Immune response in a nutshell: (Slightly simplified)

So let's start off with an infection. You either have an infected cell or bacteria in the tissue fluid for example. Both of these will have non-self antigens on their surface, which are taken up by professional antigen presenting cells. The APCs go to LYMPH NODES. Inside the lymph nodes are T cells that have undergone CLONAL SELECTION. This is when developing T cells only become "adults" if they bind to antigen the right amount, T cells that bind too weakly or too tightly are destroyed before they ever come into contact with APCs.

In the lymph nodes, APCs present the antigens to T cells, which then become activated. Activated T cells can then activate B cells and T killer cells. Activation of B cells leads to the formation of plasma cells and memory B cells (clonal expansion), and you also get memory T cells. The key thing to note here is that the activation of T cells and B cells requires what's known as co-stimulation. Basically, what this means is, if you want to activate a T cell for example, the T cell needs to bind to the antigen AND also be stimulated by cytokines.

So B cells are involved in humoral immunity and T cells are involved in cell mediated immunity. B cells secrete a load of antibodies, which can do many things, for example, they can agglutinate bacteria (agglutinins), neutralise bacteria, toxins (anti-toxins) and viruses, and also act as OPSONINS, this means they label bacteria to be targeted for phagocytosis. The general structure of an antibody is Y shaped. It has 4 chains, 2 small light chains and 2 large heavy chains. The 2 protruding bits of that Y shape have variable regions that bind to antigen, while the bit at the bottom is a constant region that binds to receptors on cells.

T cells can do loads of things. You have 2 main types, T helper cells and T killer cells. T helper cells can be divided into Th1, Th2 and T regulatory cells. Don't worry about the difference between Th1 and 2, but T regulatory cells secrete cytokines that SUPPRESS THE IMMUNE SYSTEM. They are often activated when APCs present self antigen, because obviously you don't want your immune system to target healthy cells. T killer cells essentially destroy cells that are infected. They do this by inducing apoptosis. NK cells are a type of T killer cell, they can be activated in a number of ways and are involved in the innate immune response, i.e. they don't need to be activated by a specific antigen.

Going back to our original infection, macrophages in the tissue recognise that there is something wrong and release cytokines, these cytokines can do a load of things, most notably: they stimulate inflammation, they attract neutrophils, stimulate fever, activate other cells (such as NK cells) etc. Neutrophils are the first responders during an infection, technically macrophages are there first, but only because they reside in tissues, macrophages are involved in clearing up debris mainly, neutrophils on the other hand come a long and phagocytose bacteria, the bacteria are taken up into a phagosome, which fuses with a lysosome to form a phagolysosome. Inside the phagolysosome, the bacteria are broken down (hydrolysed).

Finally, the primary immune response is essentially everything I just explained above. The secondary immune response is the same, but much quicker and much larger. Usually when you are infected, you have to wait a while to allow the right T cell to come across the right antigen. But in a secondary immune response, the right T cells are already present in the lymph nodes and tissues, so they come into contact with the antigen much quicker and can activate an immune response quicker. B cells also undergo some changes to make their antibodies bind to antigen more tightly, therefore improving the effect of B cells.

The immune response is a very complicated process, that was a very "simple" overview, and as you can see, it's not quite that simple :P But it should cover everything that is in that photo.
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AortaStudyMore
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Oops ignore that bit on clonal selection, I got it totally mixed up with something else Clonal selection is when an antigen binds to a specific complementary B cell receptor, it will eventually lead to clonal expansion
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DoubleDoors
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Thank you very much Aorta, that's really helpful!
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