Specific Defenses to Microbes

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Specific Defenses to Microbes

• B Cells and Humoral Immunity

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Review Nonspecific Defenses

• Macrophages --gt cytokines --gt fever,
  inflammation, acute phase proteins
• Neutrophils and macrophages --gt phagocytosis,
  pathogen killing
• Complement --gt opsonin, inflammation, lysis
• Interferons --gt block virus replication
• NK Cells --gt lyse virus-infected cells

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Acquired/Adaptive Immunity

• Specific resistance to certain pathogens
  (antigens)
• Discriminates foreignness (danger)
• Slow starting needs nonspecific defenses to be
  engaged
• Immune memory faster response on repeat exposure

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Acquired Immunity
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B and T Lymphocytes
B and T Cells have receptors that recognize
(bind) antigens specific to individual pathogens
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Antigens

• Antigens are foreign to host
• Proteins and large polysaccharides
• Antibodies are host proteins that bind
  specifically to antigens
• Each antigen has many epitopes antibody-binding
  sites

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Antigen binding --gt activation/proliferation --gt
effector cells memory cells
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Antibody B Cell Antigen Receptor

• Each B cell has a uniquely specific receptor
• B cells with certain receptors are produced
  randomly in the bone marrow

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Ig Gene Loci
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Antibody Binding Specificity
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Generation of B Cell Antigen Specificity
(Diversity)

• As a B cell differentiates in the bone marrow,
  gene segments are randomly selected and combined
  to encode a unique V region
• Immature B cells that bind self die by
  apoptosis
• Mature B cells go to the lymph nodes and spleen
  to await clonal selection by antigen.

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Antigen Presenting Cells

• Professional APC are
• Dendritic cells
• Macrophages
• B cells
• T cells must bind antigen presented on MHC

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B Cell Activation
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Antibody Structure

• Antibody V regions bind specific antigen
• Antibody C regions determine antibody functions

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Antibody Functions
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Antibody Functions

• Agglutination clumps pathogens, makes them
  easier to phagocytose
• Neutralization block cell binding of pathogens
  and toxins
• Opsonization coat pathogen Fc regions bind to
  Fc receptors on phagocytes
• ADCC signals killer cells to kill pathogen

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ADCCAntibody-Dependent Cell-mediated Cytotoxicity
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Immune Memory
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Natural Immune Responses are Polyclonal
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Monoclonal Antibodies

• Diagnosis
• Therapy
• Research

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Measuring Humoral Immunity

• When someone has antibodies to a pathogen, they
  are seropositive
• The amount of antibodies is the titer
• Antibodies are detected by their functions
  agglutination, neutralization, complement lysis

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Measuring Immunity

• Antibodies (IgM) agglutinate pathogens and cells

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Some Viruses Agglutinate RBC by Binding Membrane
Sugars

• Neutralizing antibodies block virus
  hemagglutination

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Humoral Immunity

• Humoral immunity is due to antibodies made by B
  cells
• Eliminates extracellular pathogens
• Works with phagocytes and complement
• Can be passively transferred

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Cellular Immunity

• Cellular immunity is due to T cells
• Eliminates intracellular pathogens, transplanted
  tissue, cancer
• Kills infected host cells
• Helps macrophages kill phagocytosed pathogens
• Difficult to passively transfer