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Biology 1202B
Brenda Murphy

1 Immunology: Adaptive (Acquired) Immunity Hematopoietic Stem Cells  Form the blood cells  Cells of the immune system Third Line of Defense Against Invasion  Adaptive (Acquired) Immune System o Specifically recognize foreign molecules & clears them from the body o Foreign molecules can be free, found on the surface of a virus, cancer cells, pollen, transplanted organs o Since the reaction is specific, it may take several days to become effective Antigen  Any foreign substance (endogenous or exogenous) that can elicit an adaptive immune response is called an antigen o Endogenous = inside of body o Exogenous = outside of body  i.e. an antigen is an antibody generator o Most common = bacteria, virus, parasites  Most are macromolecules o Large proteins (glycoproteins & lipoproteins) or polysaccharides (lipopolysaccharides) o Can be nucleic acid or synthesized molecules Antigens are Recognized by Two Types of Lymphocytes  B lymphocytes (B cells) o Differentiate from stem cells in the bone marrow o After they differentiate, they are released into the blood & carried to capillary beds serving the tissue & organs of the lymphatic system  T lymphocytes (T cells) o Produced by the division of stem cells in the bone marrow o Released into the blood & carried to the thymus (an organ of the lymphatic system) where they differentiate How do we know that Lymphocytes Recognize Antigens?  Leukocytes (WBC) in mice were killed by irradiation o Mice couldn’t develop an adaptive immune response 2  Injecting lymphocytes from normal mice into these irradiated mice restored the adaptive immune response o Injecting other cell types did not Two Types of Adaptive Immune Responses  Antibody Mediated Immunity (AMI) or Humoral Immunity o Antibody is a protein produced by the body in adaptive immunity to destroy or neutralize an antigen  Cell-Mediated Immunity (CMI) AMI & CMI Have Similar Mechanisms  Lymphocyte recognizes & binds to antigen  Lymphocyte divide to produce a large number of clones  Activated lymphocyte clears antigen from body  Activated lymphocytes differentiate into memory cells that circulate in the blood & lymph ready to initiate a rapid immune response upon seeing the same antigen, thus developing a sense of immunological memory Antibody Recognition  Each B & T cell has thousands of antigen specific, identical receptors on its plasma membrane o These are called B cell receptors (BCR) and T cell receptors (TCR) o A receptor is a protein that is either on the surface of a cell or free floating o Antigen is your foreign object that is recognized by your antibody – they are very specific to a protein o All of the receptors on a cell will be identical  Each B & T cell (with multiple identical receptors) can bind to only one particular antigen, but the entire population of B & T cells in a body can collectively recognize millions of antigens o Each antigen can be recognized by many B & T cells  We each have 10 trillion B cells that collectively have about 100 million different kinds of BCRs o These BCRs are formed before the body has encountered an antigen 3 Binding  BCR or TCR do not bind to an entire an
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