Chapter 43 | The Immune System

Immune system

Defense system of the body against foreign agents

Pathogen

Disease-causing agent

Disease

Condition that impairs normal functioning of the body

Innate immunity

Leukocytes

White blood cells

• Made in the bone marrow; stored in the lymph nodes and circulated in the blood

• Phagocytes & granulocytes

Lysozyme

Enzyme that catalyzes the breakdown of bacterial cell walls

Barrier immunity secretions

Mucous membranes & secretions:

• Lysozyme

• Saliva

• Sweat

• Tears

• Urine

All secretions have a low pH to denature foreign agents

Internal defenses

Leukocytes, interferons, and complement proteins

Phagocytes

• Recognize and bind foreign agents

• Undergo phagocytosis of foreign agents

  • Foreign agents in phagosome / food vacuole

  • Fuse with lysosome and are degraded

Granulocytes

Contain storage vesicles that contain a substance that is released when the cell is activated

Lymph nodes

Contain cells that attack viruses and bacteria

Phagocytosis

Large particulate substances or small organisms are taken up by a cell

Exocytosis

The cellular secretion of biological molecules by the fusion of vesicles containing them with the plasma membrane

Granules

Storage secretory vesicles

Cytokines

Signaling molecules of the immune system

Chemokine

Attracts other immune cells to the area (like the phagocytes)

Mast cells

Secrete histamine

Destructive enzymes

Secretion that signals to kill foreign agent (natural killer cells)

Immune cells that are both phagocytes and granulocytes

• Neutrophils

• Eosinophils

• Basophils

Toll-like receptors

Are receptors that are able to recognize features found in foreign agents

• Recognizes:

  • Flagellin and lipopolysaccharides in bacteria

  • Double-stranded RNA in viruses

  • Mannan in fungi

Inflammatory response

Histamine

A chemical that attracts other immune cells to the area

Interferons

Interfere with a virus’ ability to infect other cells:

• Cytokines that are secreted by cells infected by virus

• Act as signal to neighboring cells

• Signaling cascade turns on, synthesizes proteins that combat viral replication

Complement proteins

Bind and insert themselves into bacterial cell membranes; forming pores into foreign agent, killing it by poking it to death

Adaptive / acquired immunity

Humoral immunity

For foreign agents that have infected the body but have not infected individual cells; foreign agents are in extracellular space

Cell-mediated / cellular immunity

For foreign agents that have already entered the cells

B-cells

T-cells

Lymphocytes

Leukocytes involved in adaptive immmunity

B-cells and T-cells

• Are both lymphocytes

• Have receptor proteins on their plasma membrane that bind to a specific antigen

Antigen

Any substance (usually a molecule) that is specifically bound by an immune cell receptor

Epitope

Specific portion of antigen that the immune cell receptor binds to