Adaptive Immunity: Antigen Presentation and T-Cell Selection · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Show your insides: how T cells spot infection

Science · The Human Body · ages 21-22
Name ______________________   Date ____________

  1. A macrophage swallows a bacterium and shows its pieces. Which molecule does it use to alert helper T cells?

    • MHC class I
    • MHC class II
    • Antibody

  2. Which cells in your body do NOT carry MHC molecules?

    • Mature red blood cells
    • Macrophages
    • Dendritic cells

  3. MHC class I is found on all nucleated cells of the body.

    Circle one:   True   False

  4. During thymus selection, what happens to a young T cell that grips self strongly?

    • It is removed by apoptosis
    • It is kept as a memory cell
    • It is sent to make antibodies

  5. Why can a killer T cell destroy a virus-infected cell and spare its healthy neighbour?

    • The healthy cell hides without any MHC at all
    • Killer cells attack every cell they touch
    • Only the infected cell shows viral fragments on class I

  6. What does the positive selection step in the thymus keep?

    • Cells that ignore MHC entirely
    • Cells that interact appropriately with MHC
    • Cells that bind every self fragment

  7. Central tolerance alone catches every self-reactive T cell, so no backup controls are needed.

    Circle one:   True   False

  8. A student says B cells alert killer T cells through class I, the same route as infected tissue cells. What is the key correction?

    • B cells carry no MHC of either class
    • Killer T cells only inspect red blood cells
    • B cells use class II to activate T cells rather than flag themselves for killing
LightMySky · lightmysky.comW1-mt_8hTGqrnqGY-s1

Answer key

For grown-ups. Fold this page away before handing over the rest.

Show your insides: how T cells spot infection W1-mt_8hTGqrnqGY-s1

  1. MHC class II · Engulfed material is shown on class II to helper T cells.
  2. Mature red blood cells · Mature red blood cells lack a nucleus, so they carry no MHC display.
  3. True · Every nucleated cell shows its insides on class I for killer T cells.
  4. It is removed by apoptosis · Self-reacting cells die by negative selection, which builds central tolerance.
  5. Only the infected cell shows viral fragments on class I · Viral pieces on the display flag the infected cell, while self pieces signal safety.
  6. Cells that interact appropriately with MHC · Only cells that can read the MHC display receive the signal to mature further.
  7. False · Some self-reactive cells escape the thymus, and peripheral tolerance must quiet them.
  8. B cells use class II to activate T cells rather than flag themselves for killing · B cells are professional presenters on class II, calling helpers instead of inviting their own killing.
Worksheet · LightMySky