Adaptive Immunity (Lecture 16)

Adaptive Immunity (Lecture 16)

1. MHC & Antigen Processing

   • CLASS I
     • Endogenous antigen binding
       • From proteosome degredation
     • Present antigen to CD8+ T-cells
     • In cytoplasm
   • CLASS II
     • Exogenous antigen binding
       • From phagocytosed bacteria
     • Outside the cell
     • Present antigen to CD4+ T-cells
   • Cluster of Differentiation Molecules (CDs)
     • Used to identify/differentiate

2. T-Cells

   • Major in B-cell activation
   • T-Cell Receptors (TCRs)
     • Requires specific antigen to bind
     • Antigen presentation bridging MHC CLASS II on Antigen Presenting Cell (APC) to TCR on the T-cell
     • Initiates 1st signaling
       • MHC I w/CD8
       • MHC II w/CD4
     • 2nd signal needed for lymphocute proliferation/differentiation/expression for cytokine genes
   • Naive T-cells until matured by antigen-presentation activation
     • Proliferate
       • CD4 T-helpers
       • CD8 Cytotoxic
   • CD4 T Helper Cells
     • Activated by antigen-presentation w/MHC II
     • Th2 help B-cells produce antibodies
       • Produce specific cytokines
       • Stimulate antibody responses, defend against helminth parasites
         • Worms, tapeworms
       • Allergic reactions
     • Th1 cells promote cytotoxic activity
       • Secrete enzymes for lysis & activate macrophages
       • Mediate inflammation
   • Cytotoxic T-Cells
     • CD8+ T-cells
       • Activated by APC on MHC I
         • Kill target cells w/same antigen-MHC I combo of original activator
           • Via perforin pathway

3. B-Cells

   • Must be activated by specific antigen
     • Replicate/differentiate into plasma cells (secrete antibodies)
     • Two mechanisms
       • T-dependent
         • More effective for neutraliz. infection & more specific
         • Reqs. 2 signals for activation
           • Antigen-BCR specific int.
           • Activated Th2 binds B-cell-presented antigent, secretes B-cell growth factors
           • B-cell differenti. into plasma & memory cells
       • T-independent
         • Large identical epitopes (like LPS)
         • Less effective
           • Antibodies have low affinity for antigen
           • No memory B-cells
   • Immunoglobulic Receptors (specific)
     • When assoc w/other proteins: B-cell receptors (BCRs)

4. Antibodies