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How does an organism know the sequence of a protein?

  1. Sep 9, 2012 #1
    When a foreign protein is introduced in a rabbit or a mouse, its immune system attacks the protein by antibodies which specifically recognize the protein. How does the body know the sequence of the protein such that it manufactes an antibody which will specifically target that non-self protein.
  2. jcsd
  3. Sep 9, 2012 #2
    Lymphocytes (white blood cells) are organized in a system called the immune system. Lymphocytes recognize antigens, make antibodies specific to the antigens, and eat anything the antibodies stick to. The T cells do the initial recognition of the foreign body.
    The system is complicated. I have been trying to understand it. As I understand it as follows. Others correct me if I make a mistake (please).
    The thymus produces T cells. While the body is in an early embryo stage, the thymus “learns” to recognize all proteins that are part of the body. All proteins the thymus comes into contact with while an embryo becomes recognized as “self”. The thymus creates T cells with random sequences, where the random sequences exclude the initial set of proteins that were not part of the embryo.
    T cells are produced by the thymus. Each T-cell has a set of antibodies with randomly generated sequences. T-cells randomly come into contact with other cells. If the antigen in the other cell matches an antibody in the T-cell, the T-cell eats the other cell. The T cell makes copies of the antigen. The antigen of the consumed cell sticks out the surface of the T cell. The T cell thus “presents” the antigen of the foreign body.
    Whenever a B cell or other lymphocyte comes into contact with the activated T cell, it becomes activated against the specific antigen. The B cells pass the message along. The body treats the protein sequence described in the B cell message as an invader. The body is sensitized to the attacking protein.

    Some links and relevant quotes.
    “Killer T cells are a sub-group of T cells that kill cells that are infected with viruses (and other pathogens), or are otherwise damaged or dysfunctional.[51] As with B cells, each type of T cell recognises a different antigen. Killer T cells are activated when their T cell receptor (TCR) binds to this specific antigen in a complex with the MHC Class I receptor of another cell.”

    “A lymphocyte is a type of white blood cell in the vertebrate immune system.[1]
    Under the microscope, lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells (NK cells). Small lymphocytes consist of T cells and B cells.”

    “B cells are lymphocytes that play a large role in the humoral immune response (as opposed to the cell-mediated immune response, which is governed by T cells). B cells are an essential component of the adaptive immune system. B cells, which are the precursors of plasma cells, are characterized by the presence of a B-cell receptor able to bind specifically an antigen. Their principal functions are to make antibodies against antigens, perform the role of antigen-presenting cells (APCs) and eventually develop into memory B cells after activation by antigen interaction. Recently, a new, suppressive function of B cells has been discovered.”
  4. Sep 9, 2012 #3
  5. Sep 10, 2012 #4
    In this picture, the thymus presents a sign up sheet for embryonic proteins. The mothers placenta is the gate keeper. The proteins that reach the thymus are given stickers for parking space. Once the animals is born, the "sign up sheet" is taken away. No more stickers for parking space The off springs T cells become the gate keepers. Any protein that enters the offspring after birth, who doesn't have a sticker for parking space, has a good chance of being towed away by a white cell.
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