AJA1994
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Report Thread starter 2 years ago
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Hi I wondered if anyone could correct my understanding of immunity for AQA AS Biology unit 1 according to the syllabus. Ok here goes:

1. Phagocytes are the part of the non-specific response.
I) They are attracted to the invading pathogen by chemicals along a chemical gradient.
II) The Phagocyte binds with the pathogen and creates a vesicle around it called a phagosome.
III) A lysosome within the phagocyte fuses with the phagosome and releases its lytic enzymes causing the break down of the pathogen.
IIII) The phagocyte then presents the pathogens antigens on its surface, hence become an "antigen presenting cell." (APC)

2.
I) Helper T cells that are complementary to the antigens on the surface of the APC bind to the antigen and secrete cytokines which stimulate other complementary T cells to divide by mitosis.
II) The cloned T cells:
- Stimulate further Phagocytosis.
- Differentiate into cytotoxic T cells that kill infected cells (and hence the invading virus by secrete perforins)
- Develop into memory cells.
- Stimulate B cells to divide.

3.
I) The B cells are stimulated to divide as the cloned T cell mentioned above develops into a Helper T cell that bind to the antigens on the B cell and activates them.
II) The B cells divide by mitosis and differentiate into Plasma cells and also to Memory cells.
III) Plasma cells secrete antibodies that attach to the antigens on the pathogen and kill them by agglutination or lysis.
III) Memory Cells provide long lasting immunity by remaining in the blood for many years and activating quickly and dividing by mitosis into more memory cells and plasma cells in the presence of the pathogen, should it return.

Right so I am a little unsure as to whether this is correct, particularly the part about the cloned T cell activating the B cell. The Nelson Thorne textbook confuses me a little here. (2II)

Also a little confused if this happens ALL the time, does this full process occur for every pathogen detected? Previously I was under the impression that Cell Mediated Immunity and Humoral Immunity were completely separate as one dealt with Virus's and the other bacteria in the humor for example.

Also what, if any, is the difference between memory cells stimulated by Cell Mediated Immunity and Memory cells produced by division of B cells???

Please could someone clarify this for me please!!
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AbiCEyre
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Report 2 years ago
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In summary and in a cleared route:

T cells don't produce antibodies. The white blood cell has receptor proteins on its surface which binds to the complementary antigen, provided by a phagocyte. phagocytes activate the T cells. The helper T cell (which is a product of the T cell after it divides.) stimulates a B cell to divide into plasma cells. These plasma cells are essentially clones of B cells but secrete thousands of antibodies per second to the specific antigen detected by the T cell.

This is the primary response. When the bacteria comes around a second time there are helper T cells, memory cells and occasionally antigens which have a complementary binding site to that of the bacterium. They will then send out chemical signals to the memory cells.
- b memory cells secrete into plasma cells which secrete antibodies to attach onto the bacterium. T memory cells (as said before T cells don't produce antibodies.) activate other T cells, such as Cytoxic T cells which kill the bacteria.

Cell mediated immunity is when T lymphocytes are involved. These are manufactured in the bone marrow and matured in the Thymus gland. These do not produce antibodies. Humoral immunity is dealt by B lymphocytes, which are manufactured and matured in the bone marrow.
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