03 B Cells

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BCR

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• 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

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Activation

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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

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• macrophage antigen presenting instead

T Independent

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

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Conjugated Vaccine

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Surface Proteins

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• CD21 receptor for complement, receptor for EBV

Antibody

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Protein A

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• prevents opsonization:

Class Switching

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• 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

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• 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

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• macrophages bind to Fc very easily

IgA

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• secretory component in middle of 2 IgA

• linked by secretory: can't complement

IgA Protease

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IgE

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Somatic Hypermutation

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• Happens during proliferation after activation

• Stronger binding will proliferate the most

B Cell Fate

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Development Timeline

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Vaccines

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• active

• passive

Active

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• 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.

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Passive

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