Innate defense acts as first line of defense

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Innate Defenses Antigen Recognition

• Innate defense acts as first line of defense
• The immediate defense of the body against an
  invasion must be in the hands of preformed
  molecules, already present constitutively
• These molecules must be part of the innate immune
  system.

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Innate Defenses Antigen Recognition

• The innate immune system functions by recognizing
  highly conserved sets of molecules
• These molecular structures are specific to the
  microbes (pathogen-associated molecular patterns,
  or PAMPs) through a limited set of germ line
  encoded receptors called pattern-recognition
  receptors (PRRs)
• Adaptive immune system uses T -cell receptors
  (TCRs) and B -cell receptors (BCRs) with the
  ability to recognize a large spectrum of antigens
• There are several distinct classes of PRRs, each
  of which is involved in performing specific tasks
• These include opsonization, activation of
  complement cascade, phagocytosis, etc.

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Innate Defenses Antigen Recognition(PRRs)

• First, PRRs recognize microbial components, known
  as pathogen-associated molecular patterns
  (PAMPs), that are essential for the survival of
  the microorganism and are therefore difficult for
  the microorganism to alter
• Second, PRRs are expressed constitutively in the
  host and detect the pathogens regardless of their
  life-cycle stage
• Third, PRRs are expressed on all cells of a given
  type, and independent of immunologic memory
• Different PRRs react with specific PAMPs, show
  distinct expression patterns, activate specific
  signaling pathways, and lead to distinct
  antipathogen responses
• The basic machineries underlying innate immune
  recognition are highly conserved among species,
  from plants and fruit flies to mammals

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Innate Defenses Antigen Recognition (TLRs)

• A class of PRRs called Toll-like receptors (TLRs)
  has the ability to recognize pathogens or
  pathogen-derived products and initiate signaling
  events leading to activation of innate host
  defenses
• Signaling by TLRs initiates acute inflammatory
  responses by induction of anti-microbial genes
  and inflammatory cytokines and chemokines
• Subsequent events, such as recruitment of
  neutrophils and activation of macrophages, lead
  to direct killing of the microbes
• The notion of TLRs is primary sensors of
  pathogens and responsible for orchestrating the
  innate responses
• TLRs contribute significantly to activation of
  adaptive immune responses

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Innate Defenses Antigen Recognition

• There are 10 TLRs, named TLRs 110, known in
  mammals
• These receptors recognizes molecules derived from
  a unique class of microbial agents
• TLR4, for example, recognizes lipopolysaccharide
  (LPS), which is unique to Gram-negative bacteria
• TLR2 recognizes peptidoglycan, which is abundant
  in Gram-positive bacteria
• TLR3 recognizes double-stranded RNA from
  double-stranded viruses
• TLR7 and 8 recognize RNA from single-stranded
  viruses
• TLR9 recognizes unmethylated CpG DNA found
  abundantly in prokaryotic genomes and DNA viruses

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Host-Pathogen Interplay

• Despite this armory of ready-made weapons, the
  fact that specific immune antibody is required to
  prevent some infections
• Often this is because the invading organism has
  evolved some mechanisms for escaping destruction
• Examples of this include the capsule of certain
  bacteria which prevents innate recognition. Some
  species of bacteria and protozoa actually welcome
  phagocytosis, having devised means of surviving
  inside the phagosome or cytoplasm of the cell,
  phagocytosis helps hide them from other immune
  mechanisms
• Because of their short generation times pathogens
  will always hold an advantage in the cat and
  mouse game of immunity.

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Adaptive immune responseCells Associated

• T cells
• B cells
• Dendritic Cells
• Other Effector cells

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Adaptive Defenses T Lymphocytes

• T lymphocytes constitute the "cellular" arm of
  acquired/specific immunity
• T lymphocytes play a central role in controlling
  the acquired immune response
• serve as crucial effector cells through antigen
  specific cytotoxic activity and the production of
  soluble mediators called lymphokines (the
  cytokines produced by lymphocytes)
• There are two major subsets of T lymphocytes that
  differ in effector function, MHC restriction and
  accessory molecule usage

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Adaptive DefensesT cell receptors

• T lymphocytes express a clonal antigen-specific
  receptor
• Each T cell posses just one type of receptor, so
  that all of the receptors from one cell can only
  recognize one antigen
• The T cell receptor (TCR) is in fact very similar
  to Immunoglobulin
• It has 2 paired polypeptide chains both of which
  have constant and variable portions and both of
  which are composed of immunoglobulin-like domains
• Two important differences are
• a) TCR is monovalent
• b) It exists only as a cell surface receptor and
  has no counterpart to secreted antibody
• Unlike immunoglubolin, they are MHC restricted

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Adaptive DefensesT cell receptors
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Adaptive DefensesT cell receptors