AGING AND THE
LYMPHATIC SYSTEMThe aging of the lymphatic system is apparent in the
decreased efficiency of immune responses. Elderly
people are more likely than younger ones to develop
shingles, when an aging immune system cannot keep
the chickenpox virus dormant. They are also more
susceptible to infections such as influenza and to what
are called secondary infections, such as pneumonia
following a case of the flu. Vaccines for both of these
are available, and elderly people should be encouraged
to get them. Elderly people should also be sure to get
a tetanus-diphtheria booster every 10 years.
Autoimmune disorders are also more common
among older people; the immune system mistakenly
perceives a body tissue as foreign and initiates its des-
truction. Rheumatoid arthritis and myasthenia gravis
are examples of autoimmune diseases. The incidence
of cancer is also higher. Malignant cells that once
might have been quickly destroyed remain alive and
proliferate.The Lymphatic System and Immunity 337BOX14–6 VACCINES THAT HAVE CHANGED OUR LIVES
they are no longer possible reservoirs or sources of
the pathogen for others, and the spread of disease
may be greatly limited.
Other diseases that have been controlled by the
use of vaccines are tetanus, mumps, influenza,
measles, and German measles. Whooping cough
had been controlled until recently, when the vacci-
nation rate decreased; the annual number of cases
in the United States has more than doubled. The
vaccine for hepatitis B has significantly decreased
the number of cases of this disease among health-
care workers, and the vaccine is recommended for
all children. People who have been exposed to
rabies, which is virtually always fatal, can be pro-
tected by a safe vaccine.
Without such vaccines our lives would be very
different. Infant mortality or death in childhood
would be much more frequent, and all of us would
have to be much more aware of infectious diseases.
In many parts of the world this is still true; many of
the developing countries in Africa and Asia still can-
not afford extensive vaccination programs for their
children. Many of the diseases mentioned here,
which we may rarely think of, are still a very signif-
icant part of the lives of millions of people.In 1797, Edward Jenner (in England) published his
results on the use of the cowpox virus called vac-
cinia as the first vaccine for smallpox, a closely
related virus. (He was unaware of the actual patho-
gens, because viruses had not yet been discovered,
but he had noticed that milkmaids who got cow-
pox rarely got smallpox.) In 1980, the World Health
Organization declared that smallpox had been
eradicated throughout the world. A disease that
had killed or disfigured millions of people through-
out recorded history is now considered part of his-
tory (except for the possible use of the virus as a
biological weapon).
In the 19th century in the northern United
States, thousands of children died of diphtheria
every winter. Today there are fewer than 10 cases
of diphtheria each year in the entire country. In
the early 1950s, 50,000 cases of paralytic polio
were reported in the United States each year.
Today, wild-type polio virus is not found in North
America.
Smallpox, diphtheria, and polio are no longer
the terrible diseases they once were, and this is
because of the development and widespread use of
vaccines. When people are protected by a vaccine,Table 14–2 TYPES OF IMMUNITY
Type Description
GeneticAcquired
Passive
NATURALARTIFICIALActive
NATURALARTIFICIAL- Does not involve antibodies; is
programmed in DNA - Some pathogens affect certain
host species but not others - Does involve antibodies
- Antibodies from another source
- Placental transmission of antibodies
from mother to fetus - Transmission of antibodies in
breast milk - Injection of preformed antibodies
(gamma globulins or immune
globulins) after presumed exposure - Production of one’s own antibodies
- Recovery from a disease, with pro-
duction of antibodies and memory
cells - A vaccine stimulates production of
antibodies and memory cells