Three Lines of
Defense - the skin, roaming cells that attack and engulf pathogens, and
the highly specific immune system.
Skin: The First Line of Defense (Fig. 33.1)
skin is the largest organ of the body and is composed of three layers. (Fig. 33.2)
Other External Surfaces
sticky mucus and cilia
Counterattack: The Second Line of Defense
The Lymphatic System (Fig. 33.3)
Cells That Kill Invading Microbes: all white blood cells
Proteins That Kill Invading Microbes
system is made up of a series of inactive plasma proteins that become activated
when they encounter fungi and bacteria in the body.
Complement proteins (Fig. 33.6)
The Inflammatory Response (Fig. 33.7)
chemical alarm signal
The Temperature Response
Specific Immunity: The Third Line of Defense
Leukocytes (white blood cells) include macrophages, neutrophils and natural killer cells
B cells and T cells are also called lymphocytes
helper T cells: initiate the response
memory T cells: provide a quick response to infection
cytotoxic T cells: lyse infected cells
suppressor T cells: stop the immune response
cells can only bind to antigens on the surface of cells.
memory B cells.
Initiating the Immune Response
Antigen-presenting cells (Fig. 33.8)
interleukin-1 activates the helper T cells, which in turn activate both T cells and B cells, by releasing interleukin-2.
T Cells: The Cellular Response (Fig. 33.9)
mobilizes a type of T cell known as a cytotoxic T cell.
special receptor protein
clone of cells
also activates B
cells to attack bacteria
receptor proteins called antibodies. (Fig. 33.11)
clone of B cells
memory B cells
Summary Movie of the specific immune system response.
immune system is able to recognize virtually every foreign molecule with which it comes
Active Immunity Through Clonal Selection
primary immune response (Fig. 33.13)
secondary immune response
Summary of immune response (Fig. 33.14)
vaccination (Fig. 33.15)
dead or disabled pathogen
"piggyback" vaccines (Fig. 14.11)
Flu. Flu epidemic of 1918 (Fig. 33.16). 20 million Americans and Europeans died in 18 months.
HIV vaccine (Fig. 33.17)
Immune System Failure
Autoimmune diseases represent failures of the immune system. Sometimes the immune
system begins to attack specific cells in the body, as it does in diabetes,
rheumatoid arthritis, and multiple sclerosis.
Allergies. (Fig. 33.20)
mast cells release histamines that trigger mucus production and nasal congestion. (Movie)
Common allergens include feces of dust mites (Fig. 33.19), pollen, foods, fur, and other by-products of living organisms.
AIDS: Immune System Collapse
AIDS (Acquired Immune Deficiency Syndrome) is caused by HIV
T4 cell survival (Fig. 33.21).
HIV: blood, semen, and vaginal secretions have large quantities of macrophages, so HIV is transmitted
primarily through sharing intravenous
drug needles or through sexual
Tears, saliva, and urine have very low levels of macrophages, so transmission of HIV through casual touching, kissing, or using toilets is highly unlikely.
protease inhibitors, AZT
To reduce chances of contracting AIDS:
Don't reuse needles
Abstain from sex.
Have a monogamous relationship with a partner known to be free of HIV.
Use latex or polyurethane condoms.