What is pertussis toxin PT Produced by B. pertussis only when the organism is exposed to elevated te

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Disease course

• Introduction of B. pertussis to the respiratory
  tract
• Attachment to ciliated cells mediated by various
  adhesins (Fha, pili etc.)
• Immobilization and selective destruction of the
  cilia by tracheal toxin allowing bacterial
  survival and colonization in the respiratory
  tract
• Inflammatory responses - mucous accumulation in
  the tracheal and bronchial space - Coughing
• Endotoxin induces IL1, TNFa which cause fever in
  the host (Fever)PT induces lymphocytosis,
  histamine sensitization, immuno-suppression
  etc)Adenyl cyclase (Antiphagocytic)
• B. pertussis normally does not invade the cells
  of the respiratory tract, blood vessel, or
  alveoli (no sepsis or systemic infection)
• Gradual immune response starts to clear bacteria
• Convalescence or complication (bacterial
  superinfection, convulsion, hemorrhage, anoxia
  etc.)
• Once recovered, it usually provides life-long
  immunity to the patient

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Why does B. pertussis produce various toxins or
virulence factors only when it enters the human
host?

• The expression of virulence-related genes is
  temperature dependent. B. pertussis produces
  toxins or virulent factors when the environmental
  temperature is raised to 37C.
• At 25C, the membrane associated regulatory
  protein (BvgS) is inactive as are other genes
  that encode for virulence factors (Fha, PT,
  adenyl cyclase).
• At 37C, BvgS autophosphorylates and activate a
  cytoplasmic regulatory protein called BvgA by
  phosphorylation. This activate, directly or
  indirectly, transcription of BvgS, BgvA, Fha,
  pili and Act.

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What is pertussis toxin (PT)? Produced by B.
pertussis only when the organism is exposed to
elevated temperatures (body temperature)
Pertussis toxin (PT) is an A-B type exotoxin,
consisting of 1 molecule of subunit A and 5
molecules of subunit B.
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What is its mode of action?

• Affects different functions in different cells.
  The toxin is also known as histamine-sensitizing
  factor, lymphocytosis-promoting factor, and
  islet-activating protein.
• Subunit B (S-2 and S3) of PT mediates attachment
  of the toxin to target cells which include
  ciliated cells and phagocytes.
• Subunit A (S1), once enters the susceptible cell,
  mediates enzymatic ADP-ribosylation of a
  particular class of G protein called inhibitory G
  protein (Gi) which regulates the inactivation of
  adenyl cyclase.
• The ADP-ribosylated Gi protein (ADPR-Gi) can no
  longer regulate the host cells ability to
  inactivate adenyl cyclase activity. The net
  result is an uncontrolled elevation of
  intracellular c-AMP level of affected host cells.
  

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What is its mode of transmission?

• By inhalation of air borne droplets that contain
  Bordetella pertussis

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