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)
The
skin is the largest organ of the body and is composed of three layers. (Fig. 33.2)
outer
epidermis
dermis
subcutaneous
layer
Other External
Surfaces
sticky mucus and cilia
Cellular
Counterattack: The Second Line of Defense
The Lymphatic System (Fig. 33.3)
Cells That Kill
Invading Microbes: all white blood cells
Macrophages (Fig. 33.4) Phagocytosis
Movie
Neutrophils
Natural
killer cells (Fig. 33.5) Killing a
cancer cell
Proteins That Kill
Invading Microbes
The complement
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)
interferon Movie
Gamma
interferon
The Inflammatory
Response (Fig. 33.7)
chemical alarm signal
macrophages
neutrophils
The Temperature
Response
Fever
Specific Immunity:
The Third Line of Defense
Cells
of the immune system (Table 33.1a) and (Table 33.1b).
Leukocytes (white blood cells) include macrophages, neutrophils and natural killer cells
MHC proteins
Antigens
B cells and T cells are also called lymphocytes
T cells:
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
T
cells can only bind to antigens on the surface of cells.
B cells
plasma cells
memory B cells.
Initiating the Immune Response
Macrophages
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)
Interleukin-2
mobilizes a type of T cell known as a cytotoxic T cell.
(Movie)
special
receptor protein
clone of
cells
B Cells: The Humoral
Response (Fig. 33.10)
Movie
Interleukin-2
also activates B
cells to attack bacteria
surface
receptors
receptor
proteins called antibodies. (Fig.
33.11)
clone of B cells
plasma
cells
memory B cells
Summary Movie
of the specific immune system response.
The vertebrate
immune system is able to recognize virtually every foreign molecule with which it comes
in contact.
Active
Immunity Through Clonal Selection
clonal selection.
primary
immune response (Fig. 33.13)
secondary immune response
Summary of immune
response (Fig. 33.14)
Vaccination (Movie)
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)
Antihistamines
Common allergens
include feces of dust mites (Fig.
33.19), pollen, foods, fur, and other by-products of living organisms.
asthma
AIDS: Immune System
Collapse
AIDS (Acquired Immune
Deficiency Syndrome) is caused by HIV
(human
immunodeficiency virus).
This was first recognized as a disease in 1981 and infected 46 million people worldwide
by the year 2002. The AIDS epidemic in the U.S. (Fig. 33.22).
macrophages
T4 cell survival (Fig. 33.21).
HIV life
cycle
Opportunistic infections: development of HIV untreated
Contracting
HIV: blood, semen, and vaginal secretions have large quantities of macrophages, so HIV is transmitted
primarily through sharing intravenous
drug needles or through sexual
contact.
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.
Testing