21- Humoral Response

• C Domain Structure

  • IgM and IgE Heavy chain: 4 lg
  • IgA, IgD, and IgG heavy chain 3 lg
• Effector Functions


  • Different C region= different effector function
  • Mediated by proteins that bind to C regions
• Isotype switch


  Change in the C heavy domain associated with the same specific V domain
• Things Antibodies Can do

  • Neutralization
  • Agglutination
  • Opsonization
  • Complement Activation
  • Antibody- Dependent Cell-Mediated Cytotoxicity (ADCC)
  • Degranulation
• Neutralization

  • Bind to pathogen and hang onto it so it can't really do anything
  • Forms a big clump
  • Most efficient method, but pathogens will quickly evolve to avoid this
• Agglutination


  • Antibodies have multiple binding sites for antigens
  • They bind and cross link multiple pathogens at a time forming a big clump
  • Makes it easier to be trapped in mucous and cleared
• Opsonization


  • Antibodies bind and interact with Fc receptors on phagocytes to enhance phagocytosis
  • Adds to capacity provided by PRRS
• Complement Activation


  • Antibodies bind and activate complement pathways
  • Results in lysis or enhanced phagocytosis
• Antibody- Dependent Cell-Mediated Cytotoxicity (ADCC)


  • Antibodies bound to Fc receptors on NK cells and granulocytes can arm these cells against pathogens
  • Can then target certain viral and tumor antigens on cell surface
• Degranulation


  • Property of igE
  • Involved in response to extracellular parasites and allergic( hypersensitivity) responses
  • Involves Fc receptor
• Fc Receptors


  • Antibodies need to interact with other immune system cells and molecules to destroy pathogens (except for neutralization and agglutination)
  • Examples: PolylgR, FcRn, FCERI
  • They use the same signalling molecules as B cell receptors (Syk)