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Lecture 23-Adaptive Immunity

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Biology 1202B
Brenda Murphy

Lecture 23: Adaptive (Acquired) Immunity Hematopoietic Stem Cells  Form all the blood cells  As well as the cells from the immune system  The key point here is that there are many different kinds of cells that play a role within the immune system and all of them originated from a stem cell. The further away from the stem cell, the more specialized these cells become. Adaptive or Acquired Immunity  The third and most complex line of defense – found only in vertebrates  Reaction is specific to foreign substance  Foreign molecules can be free, fund on the surface of a virus, cancer cells, pollen or transplanted organs  Attack is to neutralize or eliminate pathogen  Reaction is triggered by specific molecules on the pathogen that are recognized as being foreign “nonself” to the body, since it is specific it may take several days to become effective.  Body retains a memory of the first exposure to that pathogen, enabling it to respond more quickly if the pathogen is encountered again in the future Antigen  An antigen is any foreign substance (exogenous or endogenous) that can elicit an adaptive immune response o Endogenous – generated within the body, such as cancer cells o Exogenous – enter from outside of the body, such as a virus, bacteria or parasites  Antigen specifically means “antibody generator”  Most antigens are macromolecules: o Large proteins (glycoproteins and lipoproteins) o or polysaccharides (lipopolysaccharides) o Can be nucleic acid or synthesized molecules  Antigens are recognized in the body by two different types of lymphocytes – B lymphocytes (B cells) and T lymphocytes (T cells) B cells  Differentiate from stem cells in the bone marrow  After they differentiate, thy are released into the blood and carried to capillary bed serving the tissues and organs of the lymphatic system T cells  Produced by the division of stem cells in the bone marrow  Released into the blood and carried to the thymus (an organ of the lymphatic system) where they differentiate How do we recognize that lymphocytes recognize antigens?  Experiments showed that leukocytes (WBC) in mice were killed by irradiation.  These mice couldn’t develop an adaptive immunity  Injecting lymphocytes from normal mice into these irradiated mice restored the adaptive immune response  Other bodily cells did not restore the response o Ultimately, this experiment shows that lymphocytes recognize antigens because when no lymphocytes are present the mice do not have immunity. Two Types of Adaptive Immune Responses 1. Antibody mediated immunity (AMI) or humoral immunity 2. Cell-mediated immunity AMI and CMI have similar mechanisms  Lymphocyte recognizes and 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 and lymph ready to initiate a rapid immune response upon seeing the same antigen Antibody Mediated Immunity  Antibody is a protein produced by the body in adaptive immunity to destroy or neutralize an antigen Antibody Recognition  Each B and T cell has thousands of antigen specific, identical receptors on its plasma membrane. Called B-cell receptors (BCR’s) and T-cell receptors (TCR’s)  Each B and T cell (with multiple identical receptors) can bind to only one specific 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 o For example, we each have about 10 trillion B cells that collectively have about 100 million different kinds of BCRs. These BCRs are formed even before the body has encountered an antigen. Antibody Binding  BCR or TCR do not bind to an entire antigen  Instead, the variable region of BCR and TCR bind to a p
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