03 B Cells

BCR

  • FAB: fragment antigen binding
  • FC: constant
  • Made of monomer IgM antibody

  • purple: variable regions. Vary from 1 B cell to another
  • light chain: 1 constant region; heavy chain 3 constant regions
  • variable regions end in nitrogen groups; constant end in carboxyl group
  • Connected by disulfide bridges
  • macrophage Fc/protein A binds CH2-CH3 region

Heavy chain

Activation

  1. B cell crosslinked by antigen
  2. Second signal required in addition to crosslinking
  3. MHC 2 binds TCR and CD4
  4. CD40 binds CD40L: class switching
  5. B7 binds CD28: T cytokine secretion

  • macrophage antigen presenting instead

T Independent

  • so many antigen on surface, B cell activated without T

Conjugated Vaccine

Surface Proteins

  • CD21 receptor for complement, receptor for EBV

Antibody

Protein A

  • prevents opsonization:

Class Switching

  • only change Fc portion, not FAB portion

  • Cm and Cd closes
  • Cm and Cd spliced out; B starts to make Cy (IgG), Ca, Ce

IgM

  • Classical pathway: 2 C1 molecules bind together to Fc of IgM; easy to bind because so many IgM Fc together
  • Prevents attachment: very large and clumps on to pathogens
  • Weak opsonin: too big; macrophages can't get to Fc

IgG

  • macrophages bind to Fc very easily

IgA

  • secretory component in middle of 2 IgA
  • linked by secretory: can't complement

IgA Protease

IgE

Somatic Hypermutation

  • Happens during proliferation after activation
  • Stronger binding will proliferate the most

B Cell Fate

Development Timeline

Vaccines

  • active
  • passive

Active

  • Live attenuated: T cell mediated response
  • Killed: antibodies against HA antigens of virus
  • Inactivated viral vaccines do not infect host cells and therefore do not enter the MHC class I antigen-processing pathway, which is normally required for the generation of a significant CD8+ cell-mediated immune response. In contrast, live-attenuated viral vaccines strongly stimulate the MHC class I antigen-processing pathway and can generate cytotoxic CD8+ T lymphocytes that kill infected cells.

Passive

  • give if suspicion for rabies, tetanus: neutralize before infection happens