The Immune System Chapter 43

The Immune System  An animal must defend itself against:  Viruses, bacteria, pathogens, microbes, abnormal body cells, toxins, and other foreign substances  Innate immunity is present at birth  Acquired immunity develops after exposure to foreign substances

Innate Immunity  External defenses/Non-Specific include skin, mucous membranes, and antimicrobial proteins like lysozyme, an enzyme that digests the cell walls of bacteria.  Phagocytic Cells attach to invaders and eat them, they include:  Neutrophils: the most abundant white blood cell  Macrophages: “big eaters”  Eosinophils: attack parasites  Dendritic Cells: ingest microbes

Innate Immunity  Interferons are proteins that protect against viruses  An inflammatory response is triggers when tissue is damaged  Mast cells in tissue release histamines which increase blood flow to the injured site

Innate Immunity  Natural Killer Cells patrol the body and attack virus- infected body cells and cancer cells.

Acquired Immunity  An antigen is a foreign molecule that triggers an immune response  Binding sites on antigens are called epitopes, this is where antibodies attach. They fight the invaders.

Lymphocytes  Lymphocytes are white blood cells. They are found in our blood, and fight antigens. They are made in our bone marrow.

B cells  B cells are a type of lymphocyte that mature into plasma cells that produce antibodies. Antibodies are specific towards a particular antigen and mark it for destruction.  B cells make up our humoral immune response

T cells  T cells can bind with fragments of antigens. They bind to surface proteins.  They make up the cell-mediated immune response and destroy invaders.

Types of T cells  Some T cells have the CD4 protein on them, and they are called “helper T cells”  Other T cells have the CD8 protein on them, and they are called cytotoxic or “killer T cells”

Types of Antibodies  Antibodies are shaped like the letter Y and bind to antigens. There are 5 classes:  IgM  IgG  IgA  IgE  IgD

IgM  IgM respond first to antigen exposure, and attempt to neutralize them.

IgG  IgG: Most abundant antibody in the blood, crosses placenta to give passive immunity to fetuses.

IgA  IgA: present in tears, saliva, breast milk, and mucus

IgE  IgE: triggers release of histamines in response to allergic reactions

IgD  IgD: present on B cells, binds to antigens, stimulates B cell production

Active vs. Passive  Active immunity develops after exposure to an infectious agent, or through immunization or vaccination.  Passive immunity is when antibodies from one person are transferred to another, uninfected, person (usually mom to fetus)

Allergies  Allergies are exaggerated (hypersensitive) responses to certain antigens called allergens.  An acute allergy is called anaphylactic shock which can cause breathing problems and possibly death.