The Immune Response

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The Immune Response

• Introduction
• Duality of Immune System
• Antigens Antibodies
• T-Cells Cell Mediated Immunity

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Immunology - Introduction

• Innate resistance genetically predetermined
  resistance
• Immunity ability of host to counteract specific
  substances or organisms
• Antigens - foreign substances that interact with
  the immune system

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Immunology - Introduction

• Immunity is acquired
• Naturally
• From infection natural active
• From mother to fetus natural passive
• Artificially
• From vaccination artificial active
• From immunoglobin injection artificial passive

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Immunology Introduction

• Vaccines made from pathogens
• Attenuated
• Inactivated
• Killed
• Serum
• Antiserum if contains antibodies
• Serum is separated into fractions the fraction
  containing antibodies is the gamma fraction
  gamma globulin

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Immunology Lymph System

• Bone morrow
• Thymus gland
• Spleen
• Lymph nodes

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Immunology Lymph System

• Bone morrow
• Thymus gland
• Spleen
• Lymph nodes

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Immunology Duality

• Two parts to immune response
• Humoral
• Cell Mediated
• Usually accomplished by white blood cells derived
  from hemopoetic stem cells

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Immunology Duality
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Immunology Duality

• Humoral
• Mediated by B-cells (bursa) derived from stem
  cells found in bone marrow
• Produce circulating antibodies found in the gamma
  globulin fraction of blood serum
• Defend against bacteria, viruses and toxins in
  blood and lymph

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Immunology Duality

• Cell-Mediated
• Mediated by T-cells (Thymus derived, i.e. white
  blood cells that mature in the thymus gland
• Defend against intracellular viruses,
  multi-cellular parasites, transplanted tissue and
  cancer cells

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Immunology Antibodies

• Immune response characterized by interaction
  between antigens and antibodies
• Antigens
• Foreign substances
• Molecular weight gt 10,000 daltons
• Proteins, lipoproteins, glycoproteins
• Antigenic determinants are that portion of
  antigen which reacts with a specific antibody
• Antigens have many determinants
• Hapten a low molecular weight substance
  combined with a carrier molecule

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Immunology Antibodies

• Antibodies are proteins produced by B-cells in
  response to an antigen
• Antibodies have two binding sites per molecule

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Immunology Antibodies

• Antibody molecule is a dimer
• Connected by S-S- bonds
• Variable and constant region
• Fab and Fc

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Immunology Antibodies

• Antibody classes circulating antibodies consist
  of five classes
• IgG - most prevalent
• IgM 5 monomers involved in complement fixation
  agglutination
• IgA secreted protects mucosa
• IgD antigen receptors on B-cells
• IgE bind to mast cells basophils involved in
  allergic reaction

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Immunology Antibodies
IgG IgM IgA IgD IgE
Structure Monomer Pentamer Dimer Monomer Monomer
Percent in blood 80 5-10 10-15 0.2 0.002
Location Blood Lymph Intestines Blood Lymph B-cells Secretion tears, saliva, milk B-cells Mast cells Basophils
Half-life 23 days 5 days 6 days 3 days 2 days
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Immunology Antibodies

• Antibody Production
• Mature B-cells circulate in blood each producing
  a slightly different antigen receptor
• B-cells not needed undergo cell death
• B-cells becomes activated when antigen reacts
  antigen receptors on cell surface
• Activated B-cells produce a clone of plasma cells
  and memory cells

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Immunology Antibodies

• Antigen ingested by antigen presenting cell (apc)
• Antigen broken down into smaller pieces for
  presentation

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Immunology Antibodies
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Immunology Antibodies

• Macrophages (antigen presenting cell or APC)
  engulf antigens, process them internally, then
  display parts of them on their surface together
  with some of their own proteins.
• Antigen presenting cell presents antigen and
  self antigen to helper T-cell
• Self antigen keeps immune system from forming
  antibodies against itself, i.e. immune system
  will not form antibodies against a self-self
  combination

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Immunology Antibodies

• This sensitizes the T cells to recognize these
  antigens. All cells are coated with various
  substances. CD stands for cluster of
  differentiation
• For T cells there are more than one hundred and
  sixty clusters, each of which is a different
  chemical molecule that coats the surface.
• CD8 is read "CD8 positive." Every T and B cell
  has about 100,000 molecules on its surface.
• B cells are coated with CD21, CD35, CD40, and
  CD45 in addition to other non-CD molecules.
• T cells have CD2, CD3, CD4, CD28, CD45R, and
  other non-CD molecules on their surfaces.

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Immunology Antibodies

• T cells are primed in the thymus, where they
  undergo two selection processes.
• The first positive selection process weeds out
  only those T cells with the correct set of
  receptors that can recognize the MHC molecules
  responsible for self-recognition.
• Then a negative selection process begins whereby
  T cells that can recognize MHC molecules
  complexed with foreign peptides are allowed to
  pass out of the thymus..

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Immunology Antibodies

• Helper T-cell interacts between antigen
  presenting cell and B-Cell to activate B-cell to
  produce plasma cells
• Plasma cells secrete antibody

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Immunology Antibodies

• Antibody Production (continued)
• Plasma cells secrete antibody (IgG)
• Memory cells recognize antigen from previous
  encounters produce plasma cells faster
• T-cells and B-cells that react with self are
  destroyed during fetal development

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Immunology Antibodies

• Antigen-Antibody Binding
• Antigen binds to variable region forming
  antigen-antibody complex
• IgG binding inactivates viruses and toxins
• Agglutination reduces number of active particles
  and enhances phagocytosis
• Activates the complement cascade
• Opsonization enhances phagocytosis

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Immunology Antibodies

• Immunological Memory
• Circulating antibody is called titer
• First antigen contact is primary response second
  is secondary
• Scondary response is usually faster with a
  significantly greater antibody titer

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Immunology Antibodies

• Primary antibody response

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Immunology Antibodies