The Immune System

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The Immune System
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Nonspecific Body Defenses

• Responds immediately
• Intact skin
• Mucous membranes
• Inflammatory Response
• Cellular Chemicals

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Surface Protectors

• Skin, Mucous membranes
• Physical barrier
• Chemical barrier
• pH of skin pH of vagina sebum
• Stomach acid/enzymes
• Saliva/lacrimal fluids (lysozyme)
• Sticky mucus to trap invaders in
  digestive/respiratory passages

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Cells and Chemicals

• Phagocytes
• Macrophages and Neutrophils
• Engulf foreign invaders
• Natural Killer Cells (NK) to police body
• Kill cancer cells, virus-infected cells
• NOT phagocytes (think chemical warfare)

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Inflammatory Response

• Nonspecific response
• Cardinal Signs
• Redness
• Heat (inflamm set on fire)
• Swelling
• Pain

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Inflammatory Response

• Chemical alarm
• Damaged cells release histamine, kinins
• Causes blood vessels to dilate, leaky capillaries
• Activates pain receptors
• Attracts phagocytes (WBCs) to injured area
• Called Chemotaxis (cells follow chemical signal)
• Redness/heat from increased blood flow
• Also causes edema (swelling)

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Inflammatory Response

• Prevents spread of damaging agents to other areas
• Disposes of cell debris and pathogens
• Begins repair process

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Chemicals

• Complement
• Group of plasma proteins that circulate
  (inactive)
• Attach to foreign cells and puts holes in the
  cells
• Foreign cells die
• Amplifies inflammatory response
• Calls more phagocytes to area
• Cause CMs of foreign cells to stick together

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Chemicals

• Interferon
• Small proteins secreted by infected cells
• Attach to non-infected cells
• Slows down virus multiplication

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Fever

• Abnormally high body temperature
• Pyrogens increase thermostat
• Chemicals secreted by WBCs that have been
  exposed to foreign cells
• Mild-moderate fever helpful in speeding up repair
  processes in tissues

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Immune Response

• Recognizes antigens and acts to inactivate or
  destroy them
• Antigen specific
• Acts against particular pathogens
• Systemic
• Not restricted to infection site
• Has a memory
• Recognizes and mounts stronger attacks on
  previously encountered pathogens

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Antigens

• Substance that excites the immune system and
  provokes an immune response
• Foreign intruders are non-self
• Proteins
• Carbs some lipids
• Nucleic acids
• Self-antigens dont trigger immune response but
  do in other people
• Explains rejection of transplanted organs

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Haptens

• An incomplete antigen
• A small (non-antigenic molecule)
• When it links up with the bodys proteins, body
  thinks its foreign
• These are what cause allergies!

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Lymphocytes

• B and T cells
• B cells
• Mature in bone marrow
• Produce antibodies (Y-shaped)
• Oversee humoral immunity
• Antibody-mediated immunity
• T cells
• Mature in Thymus gland
• Help with cell-mediated response (dont make
  antibodies)
• Immunocompetent
• When cells can respond to a specific antigen by
  binding to it

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Lymphocytes, cont.

• Immunocompetent cells only recognize one antigen
• All receptors on the cell are the same
• Our genes determine what germs we can recognize
  and resist
• When cells are immunocompetent, they travel to
  lymph nodes/spleen to mature
• Mature cells circulate the body in search of
  antigens

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Macrophages

• Big Eaters
• Antigen presenters
• They engulf foreign particles and present them
  like flags so T cells can recognize the antigens
• Secretes proteins called monokines
• Become Killer Macrophages in response to T-cell
  activation
• Stay in lymph organs

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Humoral (Antibody-Mediated) Immunity

• Immature B cell is stimulated to mature when an
  antigen binds to its surface receptors
• Clonal selection begins
• B cell grows, multiplies to form an army of
  cloned cells
• Most of these become plasma cells
• Antibody-producing factories (produce 2,000 per
  second)

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Humoral (Antibody-Mediated) Immunity

• B cell clones that dont become plasma cells
  become memory cells
• Can respond to the antigen later
• Provide secondary response
• Faster and more effective, because attack plans
  have already been made

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Active vs. Passive Humoral Immunity

• Active
• When B cells encounter antigens and produce
  antibodies against them
• Naturally acquired during infections
• Artificially acquired through vaccines
• Most vaccines contain dead or weakened viruses
• Vaccines keep you from getting most symptoms
• Vaccines still stimulate antibody production and
  memory of antigens
• Booster shots can intensify immunity later

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Active vs. Passive Humoral Immunity

• Passive
• Antibodies are obtained from serum of immune
  human or animal
• B cells NOT challenged
• Memory does NOT occur
• Protection is temporary (ends when antibodies
  degrade in body)
• Natural Passive immunity
• When moms antibodies cross placenta into fetal
  circulation
• Artifical Passive immunity
• When someone receives immune serum/gamma globulin
• (Hepatitis, snake bites, botulism, rabies,
  tetanus)

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Monoclonal Antibodies

• Produced by descendants of a single cell
• Are antibodies that are specific for one antigen
• Used to deliver cancer-fighting drugs
• Also used to diagnose Hepatitis, Pregnancy,
  Rabies, as well as for early cancer detection

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Antibodies

• AKA Immunoglobulins (Igs)
• Blood proteins
• Proteins secrected by activated B cells or
  plasma-cell offspring in response to an antigen
• Capable of binding with that antigen
• Formed in response to antgens

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Antibodies

• Made of 4 Amino Acid chains linked by disulfide
  bonds
• Two heavy chains and two light chains (1/2 the
  size of heavy chains)
• The chains combine to form the antigen-binding
  site that fits its specific antigen

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Antibodies

• 5 classes (Remember MADGE)
• IgM IgA IgD IgG IgE
• IgD is virtually always attached to B cells
• IgG is only one that can cross placenta
• Also the most abundant
• IgA is found in mucus and other secretions
• IgM, IgG can fix complement
• IgE are trouble-makers in allergies

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Antibody Function

• Inactivate antigens
• Complement fixation (activation)
• Triggers events that cause lysis of foreign cells
• Neutralization
• When antibodies bind to sites on foreign cells to
  cause cell injury
• Blocks harmful effects of toxins produced by
  bacteria/virus
• Agglutination
• Causes clumping of foreign cells (think Blood
  Transfusion reactions)
• Precipitation
• When antigen-antibody complexes are so big that
  they cant stay dissolved in solution (makes them
  easily captured)

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Cell-Mediated Immune Response

• T cells cant bind with free antigens like B
  cells
• They must recognize an antigen presented by a
  macrophage AND self by binding to the
  macrophage
• The macrophage feeds antigens to the T cell
  (kind of like a double handshake)

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Classes of T cell Clones

• Cytotoxic (Killer) T Cells
• Specialize in killing virus-infected, cancer
  cells, or foreign graft cells (inject toxic
  poison into CM)
• Helper T Cells
• Directors/Managers of Immune System
• Circulate and recruit other cells to fight
• Stimulate B cells to divide
• Signal for antibody production
• Release chemicals that rid body of antigens
• Stimulate B and T cells to grow/divide
• Attract more WBCs to area
• Enhance macrophages ability to destroy microbes
  (cause insatiable appetite for them)

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Classes of T Cell Clones, cont.

• Suppressor T Cells
• Release chemicals that suppress activity of T and
  B cells
• Help wind down/stop immune response after the
  antigen is destroyed
• Delayed hypersensitivity T Cells
• Play a role in allergies and long-term
  inflammations
• Memory Cells
• Provide memory for each antigen encountered to
  allow the body to respond quickly next time

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Organ Transplants

• 4 Types of Grafts
• Autografts
• Transplanted from one place to another in same
  person IDEAL
• Isografts
• Tissue grafts donated by identical twin IDEAL
• Allografts
• Taken from unrelated person Blood Typing/antigen
  matching must happen (at least 75 match)
• Xenografts
• Harvested from another species NEVER SUCCESSFUL
• Immunosuppressive Therapy
• Drugs, radiation (severe side effects)
• Body cant protect itself against foreign
  antigens
• Most frequent cause of death is by
  bacterial/viral infection

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Allergies

• AKA Hypersensitivities
• Abnormal vigorous immune response to a perceived
  threat that is harmless
• Allergen is a type of antigen that causes this
  response
• Immediate (acute) Hypersensitivity
• Runny nose, watery eyes, itching, hives,
  restricted air flow (inhaled allergen)
• Anaphalactic Shock
• When allergen directly enters bloodstream and
  travels through body
• Reaction involves the whole body

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Allergies, cont.

• Delayed Hypersensitivity
• Take days to appear (1-3)
• Allergic contact dermatitis (poison ivy, contact
  with heavy metals, cosmetics, deodorant)
• Skin tests for TB depend on this type of reaction

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Immunodeficiencies

• SCID (Severe Combined Immunodeficiency Disease)
• Congenital
• Not enough B and T cells
• Minor infections are lethal
• AIDS (Acquired Immunodeficiency Syndrome)
• Interferes with Helper T cell activity

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Autoimmune Diseases

• Occurs when the body produces antibodies and T
  cells that attack and damage its own tissues
• Triggers
• Inefficient lymphocyte programming (self-reactive
  immune cells arent eliminated)
• Hidden antigens or new self-antigens caused
  by mutation or damage to cell
• Reaction of antibodies produced against foreign
  antigens with self-antigens (Strep antibodies can
  react with heart antigens and cause rheumatic
  fever)