12.8.4 Immune Response: An Overview

Question 1

Immune Response: An Overview

Answer 1

• Major histocompatability complex (MHC) molecules are glycoproteins found on the surface of cells. There are two major classes of MHC molecules—class I MHC and class II MHC molecules.
• Cytotoxic T cells are activated by antigens displayed on class I MHC molecules on the surfaces of nucleated cells. Helper T cells are stimulated by antigens presented on class II MHC molecules on the surface of macrophages.
• The specific immune response involves the activation of B cells, helper T cells, and cytotoxic T cells by antigens that are present in the body.

Question 2

class I & II MHC molecules

Answer 2

• Class I MHC molecules serve as antigen presenters on all nucleated body cells. Class I MHC molecules display antigen fragments on the surface of infected cells. The antigen-MHC I complex is able to activate cytotoxic T cells.
• Class II MHC molecules serve as antigen presenters on
  macrophages, B cells and activated T cells, and on cells inside of the thymus. Class II MHC molecules display antigen fragments on the surfaces of these cells. The antigen-MHC II complex is able to activate helper T cells.

Question 3

note

Answer 3

- The diagram to the left shows an overview of the specific immune response. After the first exposure to an antigen, macrophages may engulf and present the antigen to helper T cells (down the middle of the illustration). The combination of class II MHC molecule and antigen activate helper T cells. Once activated, helper T cells will clone, producing more helper T cells and memory helper T cells specific for that antigen. Activated helper T cells will also release cytokines
that will stimulate both B cells and cytotoxic T cells.
- On the right side of the diagram, infected body cells present antigen fragments on class I MHC molecules to cytotoxic T cells. This presentation will activate cytotoxic T cells to clone form active cytotoxic T cells and memory T cells against the antigen.
- B cells (shown on the left side of the diagram) are directly activated by free antigen to clone into plasma and memory cells.

Question 4

Foreign antigens that are processed within infected body cells are presented by ___________ to ____________.

Answer 4

• class I MHC molecules; cytotoxic T cells

Question 5

Which of the following statements about helper T cells is incorrect?

Answer 5

• Helper T cells produce antibodies.

Question 6

The activated B cell forms a ____________________, which produces antibodies, and clones itself to form ___________________________.

Answer 6

• plasma cell; memory cells

Question 7

Foreign molecules that cause an immune response are called:

Answer 7

• antigens

Question 8

What type of molecules are MHC molecules?

Answer 8

• Glycoproteins

Question 9

What is the difference between Class I and Class II MHC molecules?

Answer 9

• Class I MHC molecules are found on all nucleated cells and Class II MHC molecules are found on macrophages, B cells and activated T cells.

Question 10

Which of the following statements about cytoxic T cells is true?

Answer 10

• Cytoxic T cells are activated by antigens presented by Class I MCH molecules.
• Cytoxic T cells form activated cytoxic T cells, which kill infected cells.
• Cytoxic T cells clone to form memory cells

Question 11

True or false?

B cells are involved in the humoral immune response and T cells are involved in the cell-mediated immune response.

Answer 11

• true