barriers that make up the first
line of defense, several internal
mechanisms serve as a second line
of defense. These mechanisms in-
clude (1) antimicrobial chemicals,
3), (3) inflammation, and (4) fe-
explains all four
mechanisms in greater depth.
There are four types of anti-
microbial substances (Figure 12.7a). Complement pro-
teins from blood form holes in microbial membranes,
which causes them to burst. Interferons are proteins
produced by lymphocytes, macrophages, and fibroblasts
that migrate to infected cells and interfere with viral rep-
lication. Iron-binding proteins inhibit the growth of
certain bacteria by reducing the amount of available iron.
Antimicrobial proteins are short peptides that kill mi-
crobes and attract other cells that participate in immune
responses. When microbes penetrate the skin and mucous
membranes or bypass the antimicrobial defenses in the
blood, the next nonspecific defense consists of phagocytes
and T cells and B cells (Figure 12.7b).
Inflammation (Figure 12.7c) is a defensive response
of the body to tissue damage. Because inflammation is
one of the body’s innate defenses, the response of a tissue
to a cut is similar to damage caused by burns, radiation,
process by which
particulate matter; the
ingestion and destruc-
tion of microbes, cell
debris, and other
The seco n d line o f in n ate im m unity • Figure 12.7
Various mechanisms, including chemicals, killer cells, inflammation, and fever,
make up a second line of defense when microbes get past surface barriers.
Complement proteins from blood become
activated and form holes in microbial
membranes, thereby causing them to burst
(cytolysis). Complement also
to a site (chemotaxis).
Enhancement of phagocytosis v____
by coating with C3b
Bursting of microbe due to inflow of
extracellular fluid through channel formed
by membrane attack complex C5-C9
Lymphocytes, macrophages, and fibroblasts infected with viruses
produce proteins called interferons that interfere with viral
replication. Interferons diffuse from one cell to another, rendering
the receiving cells resistant to the viruses.
Antimicrobial proteins (AMPs) are short peptides that
kill microbes and attract mast cells and dendritic
cells, which participate in immune responses.
Microbes do not develop resistance to AMPs as they
often do to antibiotics.
Iron-binding proteins reduce
available iron and inhibit the
growth of microbes.
These proteins include:
in red blood
in blood and
in the liver,
spleen, and red bone
in milk, saliva,
352 CHAPTER 12
The Lymphatic System and Immunity