Chapter 9 | The Immune System

  1. Figure 9.11 Which of the following statements about T cells is false?
    1. Helper T cells release cytokines while cytotoxic T cells kill the infected cell.
    2. Helper T cells are CD4+, while cytotoxic T cells are CD8+.
    3. MHC II is a receptor found on most body cells, while MHC I is a receptor found on immune cells only.
    4. The T cell receptor is found on both CD4+ and CD8+ T cells.
      Illustration shows activation of a C D 4 plus helper T cell. An antigen-presenting cell digests a pathogen. Epitopes from this pathogen are presented in conjunction with M H C I I molecules on the cell surface. A T cell receptor and a C D 8 receptor, both on the surface of the T cell, bind the M H C I I epitope complex. As a result, the helper T cell becomes activated and both the helper T cell and antigen-presenting cell release cytokines. The cytokines induce the helper T cell to clone itself. The cloned helper T cells release different cytokines that activate B cells and C D 8 plus T cells, turning them into cytotoxic T cells. The cytotoxic and binds the M H C I epitope complex on an infected cell. The cytotoxic T cell then releases perforin molecules, which form a pore in the plasma membrane, and granzymes, which break down proteins, killing the cell.
      Figure 9.11 Naïve CD4+ T cells engage MHC II molecules on antigen-presenting cells (APCs) and become activated. Clones of the activated helper T cell, in turn, activate B cells and CD8+ T cells, which become cytotoxic T cells. Cytotoxic T cells kill infected cells.
  2. Figure 9.14 Based on what you know about MHC receptors, why do you think an organ transplanted from an incompatible donor to a recipient will be rejected?
    Healthy, uninfected cells present M H C I on their surface. A natural killer cell recognizes the M H C I and does not kill the cell. An infected cell that does not produce M H C I is killed.
    Figure 9.14 Natural killer (NK) cells recognize the MHC I receptor on healthy cells. If MHC I is absent, the cell is lysed.
  3. Figure 9.16 The Rh antigen is found on Rh-positive red blood cells. An Rh-negative female can usually carry an Rh-positive fetus to term without difficulty. However, if she has a second Rh-positive fetus, her body may launch an immune attack that causes hemolytic disease of the newborn. Why do you think hemolytic disease is only a problem during the second or subsequent pregnancies?
    Illustration shows activation of a B cell. An antigen on the surface of a bacterium binds the B cell receptor. The b cell engulfs the antigen, and presents an epitope on its surface in conjunction with a M H C I I receptor. A T cell receptor and C D 4 molecule on the surface of a helper T cell recognize the epitopes M H C I I complex and activate the B cell. The B cell divides and turns into memory B cells and plasma cells. Memory B cells present antigen on their surface. Plasma B cells excrete antigen.
    Figure 9.16 After initially binding an antigen to the B cell receptor (BCR), a B cell internalizes the antigen and presents it on MHC II. A helper T cell recognizes the MHC II–antigen complex and activates the B cell. As a result, memory B cells and plasma cells are made.

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