Active Recall 1

  • Adaptive immunity is activated when innate immunity fails to fight an infection.

  • Properties: 1. Highly specific to specific inducing pathogens

  1. Memory → long-lasting protection

  2. Non-reactive to self antigens → Able to recognize own antigens from foreign ones.

  • MHC I: - All nucleated cells expressed on this molecule

  • Antigen source: Endogenous/Intracellular antigens

  • Target cell: CD8+ cytotoxic T-cells

  • Antigen origin: Foreign proteins synthesized in host cells e.g. viral proteins from virus

  • Immune response: 1. The MHC II-antigen complex is transported to surface of the cell after it is loaded with viral protein.

  1. CD8+ cytotoxic T-cells recognizes foreign protein presented by MHC I and will be activated.

  2. Once activated, CD8+ cytotoxic T-cells will release cytokines, perforin and granzymes to induce apoptosis (cell death) in infected cell

  3. Some CD8+ cytotoxic T-cells will differentiate into memory T-cells to provide long-lasting immunity by enabling a stronger and faster response against the same antigen.

  • MHC II: Antigen Presenting Cells (APCs) are expressed on this molecule.

  • APCs: Dendritic Cells, B-cells (produce antibodies), Macrophages (phagocytic activity)

  • Target cell: CD4+ Helper T-cells

  • Antigen source: Exogenous antigens

  • Antigen origin: Antigen taken up from environment outside of APCs.

  • Immune response: 1. B-cells, macrophages get activated.

  1. Support the CD4+ Helper T-cells activation to release cytokines which promote proliferation and differentiation of CD8+ cytotoxic T-cells into effector cytotoxic T-cells