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PSL301H1 (21)


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University of Toronto St. George
Shaun Burns

AQUIRED IMMUNITY (814-818) • Acquired immune responses are antigen-specific responses o Body recognizes a certain foreign substance and reacts specifically against it  Mediated primarily by lymphocytes o Active immunity  Occurs when body is exposed to a pathogen, then produces its own antibody  Can occur when a pathogen naturally invades body, or via vaccination o Passive immunity  Occurs when antibodies are acquired from another animal  Not permanent • 3 main types of lymphocytes o Cells can be distinguished from each other by their specific membrane receptors  Makes them exclusive to certain ligand  Lymphocytes specific to a give ligand known as a clone • Each clone of lymphocytes is represented by a few cells, naïve lymphocytes o Continue to be generated throughout lifetime o First exposure to antigen activates appropriate clone, stimulates clonal expansion o Differentiate into effector and memory cells  Effector cells are immediate but temporary  Memory cells are long-term and self-reproducing • Subsequent exposures to antigen activate memory cells and enhance subsequent response efficiency  Few memory cells of clone remain behind after antigen has been repelled, in preparation for next response PSL301H1|Lecture 3 • o B lymphocytes  Develop in bone marrow  Activated cells develop into plasma cells • Secrete antibodies (immunoglobins) o Inserted into B cells’ membrane and become surface receptors, marking clone members o When B cells activate in response to antigen, some differentiate into plasma cells  Effector cells for B lymphocytes  Do not have antibodies bound to membrane, instead secrete own quickly o Gamma globulins  IgGs • Most common (75%) in adults, secondary immune response • Transferred across placenta from mother to baby • Activate complement  IgM • Primary immune response • Activate complement  IgA • Found in external excretions, disable pathogens before reaching interior  IgEs • Mast cells degranulate, release histamine (allergic reactions) PSL301H1|Lecture 3  Antibody proteins • Basic molecule has 4 polypeptide chains linked into a Y shape o Fab region  Light chain attached to heavy chain on each arm
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