Test cram uwu

CHAT Immune practice

FRQ 1: Viral Infection & MHC

  • A human cell becomes infected with influenza virus.

    • a) Explain how viral antigens become associated with MHC I molecules.

    • b) Identify which immune cell type will recognize this complex.

    • c) Describe what happens to the infected cell after recognition.

Notes:

  • MHC II → Helper-T cells + CD4

  • if antigen is intracellular → MHC I

  • antigen is engulfed by macrophage (extracellular) → MHC II

FRQ 2: Bacterial Infection & MHC

  • A macrophage engulfs a bacterium.

    • a) Explain how bacterial antigens become associated with MHC II molecules.

    • b) Identify which immune cell binds this complex.

    • c) Explain how this interaction contributes to both humoral and cell-mediated immunity.

Notes:

  • spike proteins → virus NOT bacteria

Answer:

  • Macrophage performs phagocytosis.

  • Bacterium enters a phagosome (special type of vesicle)

  • Phagosome fuses with lysosome → digestion.

  • Peptide fragments bind to MHC II in vesicles.

  • MHC II–peptide complex moves to membrane.

MHC 2 pathway

  • APC engulfs microbe, digests, displays parts on its surface bound to an MHC II receptor

    • MO’s will secrete IL-1 → stimulate Th cells

  • TCR (one-to-one for presented antigen) binds to MHC II/MO complex

  • CD4 receptor also binds to the side of the MHC II molecule

  • MO + Th → signal transduction → Th produces IL-2 + other immune chemicals → ACTIVATES CYTOTOXIC T CELLS

  • IL-2 binds to Th surface receptors → T-cell undergoes clonal selection

    • clonal selection → only activated cells replicate to produce cells with the same antigen

      • memory cells → secondary immune response

  • B-cells → produce antibodies

    • bind antigen with antibody receptor → take in with endocytosis → break down + display on MHC II (think macrophage)

    • CD4 + TCR → stabilize interaction (think APC w/ Th)

MHC 1 Pathway

Allergy Pathway

  • similar to MHC 2 pathway

    • allergen is taken up by APC

    • allergen is presented by MHC II

    • Th cell is activated

    • B cells are activated and undergo clonal expansion + modification

  • THE DIFFERENCE IS IN THE PRODUCTION OF ANTIBODIES

    • B cells will produce IgE antibodies specific to the allergen

    • IgE will bind to mast cells and stays attached → person becomes sensitized (1st exposure)

  • 2nd exposure

    • allergens bind to and cross-link two Abs that are already bound to mast cells → causes mast cell degranulation (release histamine + other chemicals)

Structural Map (will flesh out more later)

Clean Structural Map

Extracellular pathogen (like many bacteria)

  • Antibodies (B cells) are dominant.

  • Complement helps.

  • Phagocytes clean up.

Intracellular pathogen (like viruses)

  • Antibodies can block entry.

  • But once inside:

    • Cytotoxic T cells must kill the infected cell.

This is the big immune fork.