332 The Lymphatic System and Immunity
initiate a rapid response upon a second exposure.
Other B cells become plasma cellsthat produce anti-
bodies specific for this one foreign antigen.
Antibodies, also called immune globulins(Ig) or
gamma globulins, are proteins shaped somewhat like
the letter Y. Antibodies do not themselves destroy for-
eign antigens, but rather become attached to such anti-
gens to “label” them for destruction. Each antibodyBOX14–2 AIDS
placental transmission of the virus from mother to
fetus.
In the United States, most of the cases of AIDS
during the 1980s were in homosexual men and IV
drug users who shared syringes contaminated with
their blood. By the 1990s, however, it was clear that
AIDS was becoming more of a heterosexually trans-
mitted disease, with rapidly increasing case rates
among women and teenagers. In much of the rest
of the world, especially Africa and Asia, the trans-
mission of AIDS has always been primarily by het-
erosexual contact, with equal numbers of women
and men infected. In many of these countries AIDS
is an enormous public health problem, and the
annual number of new cases is still rising.
At present we have no medications that will
eradicate HIV, although certain combinations of
drugs effectively suppress the virus in some people.
For these people, AIDS may become a chronic but
not fatal disease. Unfortunately, the medications do
not work for everyone, and they are very expensive,
beyond the means of most of the world’s AIDS
patients.
Development of an AIDS vaccine has not yet
been successful, although dozens of vaccines are
undergoing clinical trials. A vaccine stimulates anti-
body production to a specific pathogen, but every-
one who has died of AIDS had antibodies to HIV.
Those antibodies were not protective because HIV is
a mutating virus; it constantly changes itself, mak-
ing previously produced antibodies ineffective. An
AIDS vaccine may not be entirely effective, may not
have the 80% to 90% protection rate we have
come to expect from vaccines.
If we cannot cure AIDS and we cannot yet pre-
vent it by vaccination, what recourse is left?
Education. Everyone should know how AIDS is
spread. The obvious reason is to be able to avoid
the high-risk behaviors that make acquiring HIV
more likely. Yet another reason, however, is that
everyone should know that they need not fear
casual contact with people with AIDS. Healthcare
personnel have a special responsibility, not only to
educate themselves, but to provide education
about AIDS for their patients and the families of
their patients.In 1981, young homosexual men in New York and
California were diagnosed with Kaposi’s sarcoma
andPneumocystis cariniipneumonia. At that time,
Kaposi’s sarcoma was known as a rare, slowly grow-
ing malignancy in elderly men. Pneumocystis pneu-
monia was almost unheard of; P.carinii(nowP.
jiroveci) is a pathogen that does not cause disease in
healthy people. That in itself was a clue. These
young men were not healthy; their immune sys-
tems were not functioning normally. As the number
of patients increased rapidly, the disease was given
a name (acquired immunodeficiency syndrome—
AIDS) and the pathogen was found. Human
immunodeficiency virus (HIV) is a retrovirus that
infects helper T cells, macrophages, and other
human cells. Once infected, the human cells con-
tain HIV genes for the rest of their lives. Without suf-
ficient helper T cells, the immune system is seriously
impaired. Foreign antigens are not recognized, B
cells are not activated, and killer T cells are not
stimulated to proliferate.
The person with AIDS is susceptible to oppor-
tunistic infections, that is, those infections caused
by fungi and protozoa that would not affect aver-
age healthy adults. Some of these infections may be
treated with medications and even temporarily
cured, but the immune system cannot prevent the
next infection, or the next. As of this writing, AIDS
is considered an incurable disease, although with
proper medical treatment, some people with AIDS
may live for many years.
Where did this virus come from? The latest
research suggests that HIV evolved from a harmless
chimpanzee virus in Africa sometime during the
1930s. Spread of the virus was very slow at first,
and only when air travel became commonplace did
the virus spread worldwide.
The incubation period of AIDS is highly variable,
ranging from a few months to several years.
An infected person may unknowingly spread HIV to
others before any symptoms appear. It should
be emphasized that AIDS, although communicable,
is not a contagious disease. It is not spread
by casual contact as is measles or the common
cold. Transmission of AIDS occurs through sexual
contact, by contact with infected blood, or by