Elements of the Immune System

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Elements of the Immune System

• Protective barriers
• Skin tough layer of keratinized cells
• Mucous membranes much more fragile
• Designed to allow movement across membrane
  epithelia

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Elements of the Immune System

• Protective barriers
• Skin tough layer of keratinized cells
• Mucous membranes much more fragile
• Designed to allow movement across membrane
  epithelia
• Mechanical, chemical and microbial components

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The Innate Immune System

• Always ready to respond
• Provides protection from almost all potential
  pathogens

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The Innate Immune System

• Cellular and molecular components
• Effector cells
• Phagocytes
• Macrophages
• Neutrophils
• Carry out Phagocytosis

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Phagocytosis

• Toll-like receptors (TLR) on phagocyte surface
  recognize PAMPS (pathogen-associated molecular
  patterns) on surface of pathogen

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The Innate Immune System

• Phagocytes also send out chemical signals
  (inflammatory cytokines)

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• Cytokines have several affects
• Make blood vessels leaky vasodilation
• Attract phagocytes into the site of infection
  from blood vessel
• Vasodilation also allows molecules to enter into
  infected area
• Result is called an inflammatory reaction
  (inflammation)

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• Neutrophils are also attracted into the infected
  area
• Bacterial cells are all phagocytized
• Phagocytes also engulf and remove dead body cells
  and neutrophils
• Injured tissue is repaired

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• Complement is an important molecular component of
  innate system
• Is always present (in body fluids) in an inactive
  state until needed
• Activated by the presence of most bacterial
  pathogens
• Activated complement provides an additional
  attachment mechanism for phagocytes
• Activated complement attaches to bacterial
  surface
• Phagocyte has a complement receptor that attaches
  to activated complement
• Attachment initiates phagocytosis

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Natural Killer (NK) cells

• Another cellular member of the innate immune
  system
• Phagocytosis and complement not very effective
  against many viruses

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Innate Immune Response not always successful

• Phagocytosis may not occur
• No attachment to bacterial surface
• Bacteria may not display any PAMPs
• Bacteria may have a capsule which masks PAMPS
  (e.g., pneumonia)
• http//student.ccbcmd.edu/courses/bio141/lecguide/
  unit1/prostruct/phag_pampcap.html
• Engulfed bacteria may be able to resist
  degradation (e.g., tuberculosis)
• Many viruses can not be phagocytized (no PAMPs)
• Many virus-infected cells do not stimulate
  destruction by Natural Killer cells
• Complement may not be activated
• Pathogens may simply multiply faster than they
  can be degraded
• Bacterial exotoxins can not be phagocytized, do
  not activate complement
• Tumor cells are rarely destroyed by innate immune
  response

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Innate Immune Response not always successful

• Phagocytosis may not occur
• No attachment to bacterial surface
• Bacteria may not display any PAMPs
• Bacteria may have a capsule which masks PAMPS
  (e.g., pneumonia)
• http//student.ccbcmd.edu/courses/bio141/lecguide/
  unit1/prostruct/phag_pampcap.html
• Engulfed bacteria may be able to resist
  degradation (e.g., tuberculosis)
• Many viruses can not be phagocytized (no PAMPs)
• Many virus-infected cells do not stimulate
  destruction by Natural Killer cells
• Complement may not be activated
• Pathogens may simply multiply faster than they
  can be degraded
• Bacterial exotoxins can not be phagocytized, do
  not activate complement
• Tumor cells are rarely destroyed by innate immune
  response

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Adaptive Immune System

• Phagocytosis may not occur
• Can assist phagocytes to attach to bacteria AND
  viruses
• Many virus-infected cells do not stimulate
  destruction by Natural Killer cells
• Can assist Natural Killer cells to recognize
  virus-infected cells
• Can prevent viruses from infecting to body cells
• Can directly destroy virus-infected cells
• Complement may not be activated
• Can activate complement
• Pathogens may simply multiply faster than they
  can be degraded
• Can dramatically increase speed of response
• Bacterial exotoxins can not be phagocytized, do
  not activate complement
• Can neutralize exotoxins
• Tumor cells are rarely destroyed by innate immune
  response
• Can destroy many tumor cells

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Adaptive Immune System

• Cellular components
• Lymphocytes
• B-lymphocytes
• Produce antibodies
• T-lymphocytes (3 functional groups)
• T-helper lymphocytes
• Assist B-lymphocytes and other T-lymphocytes
• Enhance phagocyte degradation of ingested
  bacterial cells
• T-cytotoxic lymphocytes
• Destroy virus-infected cells
• T-regulatory cells
• Control certain functions of the adaptive immune
  response

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Adaptive Immune System

• Cellular components
• Molecular components
• Antibodies (secreted by B-lymphocytes)
• Assist phagocytes to attach to bacteria
• Capsules antibodies attach to capsules
• No PAMPs antibodies attach to other surface
  molecule
• Phagocytes have receptors for antibody molecules

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Adaptive Immune System

• Antibodies (secreted by B-lymphocytes)
• Assist phagocytes to attach to bacteria
• Assist phagocytes to attach to viruses -gt
  phagocytosis of viruses
• Assist phagocytes to attach to exotoxins -gt
  phagocytosis of exotoxins
• Can activate complement
• Can directly neutralize exotoxin
• Can prevent viruses from attaching to body cells
• Can assist Natural Killer cells to recognize
  virus-infected cells

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Specificity of Lymphocytes

• Each lymphocyte has replicate receptors that will
  bind to only ONE molecule
• Different lymphocytes have different
  specificities
• One specificity/lymphocyte
• B-lymphocyte receptor
• Immunoglobulin
• Looks like an antibody attached to the B-cell
  surface
• T-lymphocyte receptor

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Clonal selection from pool of lymphocytes

• Literally trillions of individually specific
  lymphocytes are in the body
• Lymphocyte interacts with pathogen for which it
  is specific
• That responding lymphocyte replicates -gt expanded
  population results
• The expanded population of cells are also now
  prepared to participate in eliminating the
  pathogen more rapidly than during the initial
  encounter
• Immune system has adapted to presence of
  pathogen

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Adaptive System Tissues and Organs

• Primary Lymphoid Organs
• Where lymphocytes develop and acquire
  characteristics
• Bone marrow B-lymphocyte development
• Thymus T-lymphocyte development

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Adaptive System Tissues and Organs

• Secondary lymphoid tissues/organs
• Where lymphocytes usually function
• Lymph nodes
• Spleen
• Peyers patches (GALT)

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Secondary organs well-designed to optimize
adaptive immune responses
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Connection between Innate and Adaptive Immune
responses
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Lymphocytes circulate constantly