The Immune System: Innate and Adaptive Body Defenses
ﬂuid. Inﬂammatory chemicals are released by injured or stressed
tissue cells, and immune cells. Tey can also be formed from
proteins circulating in the blood. For example,
, a key
component of the inﬂammatory response, release the potent
Macrophages (and cells of certain boundary tissues such as
epithelial cells lining the gastrointestinal and respiratory tracts)
have special membrane receptors that allow them to recognize
invaders and sound a chemical alarm. Tese surface membrane
Toll-like receptors (TLRs)
, play a central role
in triggering immune responses. Tere are 11 types of human
±LRs, each recognizing a particular class of attacking microbe.
For example, one type responds to a glycolipid in cell walls of the
tuberculosis bacterium and another to a component of gram-
negative bacteria such as
. Once activated, a ±LR
triggers the release of inﬂammatory chemicals called
Other inﬂammatory chemicals include
inﬂammatory chemicals dilate local arterioles and make local
capillaries leakier, as we discuss next. In addition, many attract
leukocytes to the injured area and some have individual inﬂam-
matory roles as well
Vasodilation and Increased Vascular Permeability
Vasodilation accounts for two of the cardinal signs of inﬂam-
of an inﬂamed region are both due
(congestion with blood) that occurs when
local arterioles dilate.
± cells (described fully on p. 789). NK cells also secrete potent
chemicals that enhance the inﬂammatory response.
Inﬂammation: Tissue Response to Injury
Describe the inﬂammatory process. Identify several
inﬂammatory chemicals and indicate their speciﬁc roles.
is triggered whenever body tissues
are injured by physical trauma (a blow), intense heat, irritating
chemicals, or infection by viruses, fungi, or bacteria. Te in-
ﬂammatory response has several beneﬁcial eﬀects. It:
Prevents the spread of damaging agents to nearby tissues
Disposes of cell debris and pathogens
Alerts the adaptive immune system
Sets the stage for repair
of short-term, or acute, inﬂammation
set on ﬁre),
to be a ﬁ²h cardinal sign.
For instance, movement in an inﬂamed joint may be hampered
temporarily, forcing it to rest, which aids healing.
summarizes the inﬂammatory process and shows how these
cardinal signs come about.
Inﬂammatory Chemical Release
Te inﬂammatory process begins with a chemical “alarm”—a
ﬂood of inﬂammatory chemicals released into the extracellular
(a) A macrophage (purple) uses its cytoplasmic extensions
to pull rod-shaped bacteria (green) toward it.
electron micrograph (4800
(b) Events of phagocytosis.
to pathogens or debris.
eventually engulf the
particles, forming a
Lysosome fuses with
the phagocytic vesicle,
forming a phagolysosome
digest the particles,
leaving a residual body.
Exocytosis of the