Page 271 - Review of Medical Microbiology and Immunology ( PDFDrive )

mebooksfree.com

mebooksfree.com
mebooksfree.com
mebooksfree.com
mebooksfree.com
mebooksfree.com mebooksfree.com mebooksfree.com mebooksfree.com H A P mebooksfree.com mebooksfree.com
mebooksfree.com
33
C
E
R
T

Host Defenses

mebooksfree.com mebooksfree.com mebooksfree.com Pearls mebooksfree.com mebooksfree.com mebooksfree.com

CHAPTER C ONTENT S

8. Circumcision
Introduction
Nonspecific Defenses
9. Factors That Modify Host Defenses
Specific Defenses
1. Alpha & Beta Interferons
2. Natural Killer Cells
1. Active Immunity
2. Passive Immunity
3. Phagocytosis
3. Herd Immunity
4. α-Defensins
5. Apolipoprotein B RNA-Editing Enzyme (APOBEC3G)
6. Fever Self-Assessment Questions
mebooksfree.com
mebooksfree.com
mebooksfree.com mebooksfree.com mebooksfree.com known as type 1 interferon are induced by viruses, whereas mebooksfree.com
7. Mucociliary Clearance
Practice Questions: USMLE & Course Examinations
INTRODUCTION
gamma (T cell, immune) interferon, known as type II inter-
Host defenses against viruses fall into two major categories:
feron is induced by antigens and is one of the effectors of
(1) nonspecific, of which the most important are interfer-
cell-mediated immunity (see Chapter 58). The following
ons and natural killer cells; and (2) specific, including both
discussion of alpha and beta interferons focuses on the
humoral and cell-mediated immunity. Interferons are an
early, first-line defense, whereas humoral immunity and
Lambda (λ) interferon, known as type III interferon, is
cell-mediated immunity are effective only later because it
active against intestinal viruses, especially rotavirus and
takes several days to induce the humoral and cell-mediated induction and action of their antiviral effect (Figure 33–1).
norovirus. It reduces the long-term persistence of virus in
mebooksfree.com mebooksfree.com mebooksfree.com further. mebooksfree.com mebooksfree.com mebooksfree.com
arms of the immune response.
intestinal mucosal cells. The role of lambda interferon in
A description of how viruses evade our host defenses
human disease is uncertain and will not be discussed
appears in Chapter 32.
Induction of Alpha & Beta Interferons
NONSPECIFIC DEFENSES
The strong inducers of these interferons are viruses and
double-stranded RNAs. Induction is not specific for a
1. Alpha & Beta Interferons
particular virus; many DNA and RNA viruses are compe-
Alpha and beta interferons are a group of proteins pro-
duced by human cells after viral infection (or after expo-
finding that double-stranded RNA, but not single-stranded
RNA or DNA, is a good inducer has led to the conclusion
sure to other inducers). They inhibit the growth of viruses
that a double-stranded RNA is synthesized as part of the
by blocking the synthesis of viral proteins. They do so by tent inducers, although they differ in effectiveness. The
two main mechanisms: One is a ribonuclease that degrades
mebooksfree.com
mebooksfree.com
replicative cycle of all inducing viruses. The double-
mebooksfree.com mebooksfree.com mebooksfree.com side effects prevented its clinical use. The weak inducers of mebooksfree.com
mRNA, and the other is a protein kinase that inhibits pro-
stranded RNA poly (rI-rC) is one of the strongest inducers
tein synthesis.
and was under consideration as an antiviral agent, but toxic
Interferons are divided into three types based on the cell
microbiologic interest include a variety of intracellular bac-
of origin, namely, leukocyte, fibroblast, and lymphocyte.
teria and protozoa, as well as certain bacterial substances
They are also known as alpha, beta, and gamma interfer-
ons, respectively. Alpha and beta interferons, collectively
such as endotoxin.
260
mebooksfree.com mebooksfree.com mebooksfree.com mebooksfree.com mebooksfree.com mebooksfree.com