Effector mechanisms of humoral immunity

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• Effector mechanisms of humoral immunity

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Effector mechanisms of Abs

• Physiologic function of Abs is defence against
  extracellular microbes and microbial toxins
• Defects in Ab production result in increased
  susceptibility to infections
• Ab mediated elimination of Ags requires
  participation of other effector systems
• Produced Abs in lymphoid organs , perform their
  effector functions at sites distant from their
  production
• Many of the effector functions of Abs are
  mediated by the heavy chain constant regions of
  Igs and different isotypes serve different
  effector functions
• The requirement for Ag binding ensures that Abs
  activate various effector mechanisms only when
  they are needed

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• Neutralization of microbes and microbial toxins

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• Opsonization

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Fc receptors
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• Antibody-dependent cell- mediated cytotoxicity

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Phagocytosis
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Neonatal immunity
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Complement system
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Complement functions

• Host benefit
• opsonization to enhance phagocytosis
• phagocyte attraction and activation
• lysis of bacteria and infected cells
• regulation of antibody responses
• clearance of immune complexes
• clearance of apoptotic cells
• Host detriment
• Inflammation, anaphylaxis

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Proteins of the complementsystem (nomenclature)

• C1(qrs), C2, C3, C4, C5, C6, C7, C8, C9
• factors B, D, H and I, properdin (P)
• mannose binding lectin (MBL)

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Pathways of complement activation
LECTIN PATHWAY
CLASSICAL PATHWAY
ALTERNATIVE PATHWAY
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Components of the Classical Pathway

C4
C2
C3
C1 complex
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Classical Pathway Generation of C3-convertase
C4

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Classical Pathway Generation of C3-convertase
C2
C4a

_____ C4b2a is C3 convertase
Mg
C4b
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Classical Pathway Generation of C5-convertase
C2b
C4a

________ C4b2a3b is C5 convertase it leads into
the Membrane Attack Pathway
Mg
C3
C4b
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Lytic pathway
Generation of C5 convertase leads to the
activation of the Lytic pathway
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Components of the lytic pathway
C6
C5
C 9
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Lytic pathwayC5-activation
C5
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Lytic pathwayassembly of the lytic complex
C6
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Lytic pathwayinsertion of lytic complex into
cell membrane
C 9
C 9
C 9
C 9
C 9
C 9
C 9
C 9
C 9
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Complement Receptors

• CR-I promote phagocytosis
• CR-II coreceptor for B cell activation
• CR-III phagocytosis
• CR-IV phagocytosis

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Biological effects of C5a
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Biological properties of C-activation products
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Biological properties of C-activation products
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Opsonization and phagocytosis
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Complement levels may be decreased due to

• a( hereditary (relatively rare)
• b)acquired deficiency
• c) increased consumption
• d) decreased production
• Complement protein levels are usually increased,
  along with other unrelated proteins called acute
  phase proteins, during acute or chronic
  inflammation

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Decreased complement levels may be seen with

• Recurrent microbial infections (usually
  bacterial)
• Autoimmune diseases, including SLE and vasculitis
  
• Hereditary angioedema
• Acquired angioedema
• Various types of kidney disease, including
  glomerulonephritis, lupus nephritis, membranous
  nephritis, IgA nephropathy
• Malnutrition
• Septicemia
• Serum sickness (immune complex disease)
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