Defense Mechanisms of the Body
669
Table 18–7
Summary of Host Responses to Viruses
Main Cells Involved
Comment on Action
Nonspecifi c defenses
Anatomical barriers
Infl
ammation
Interferon
Body surface linings
Tissue macrophages
Most cell types after viruses enter
them
Provide physical barrier; antiviral chemicals
Provide phagocytosis of extracellular virus
Interferon nonspecifi cally prevents viral replication inside host cells
Specifi c defenses
Antibody-mediated
Helper
Plasma cells (derived from B cells)
that secrete antibodies
Helper T cells
Antibodies neutralize virus and thus prevent viral entry into cell
Antibodies activate complement, which leads to enhanced
phagocytosis of extracellular virus
Antibodies recruit NK cells via antibody-mediated cellular cytotoxicity
Secrete interleukins; keep NK cells, macrophages, cytotoxic T cells,
and helper T cells active; also help convert B cells to plasma cells.
Direct cell killing
Cytotoxic T cells, NK cells, and
activated macrophages
Destroy host cell via secreted chemicals and thus induce release of
virus into extracellular fl uid where it can be phagocytized
Activity stimulated by IL-2 and interferon-gamma
Plasma cortisol
Adrenal cortex
Cortisol secretion
Plasma ACTH
Blood
leukocytes
Plasma free
fatty acids
Plasma
amino acids
Hypothalamus
Anterior pituitary
ACTH secretion
Adipose tissue
Lipolysis
Liver
Retains Fe, Zn
Secretes acute
phase proteins
Muscle
Protein breakdown
Amino acid release
Bone marrow
Production and
release of leukocytes
Brain
Fever
Appetite
Food intake
Sleepiness
Fatigue
Plasma IL-1,
TNF, and IL-6
Monocytes and macrophages
Secrete IL-1,
TNF, and IL-6
Microbes, microbial products,
tissue injury, cytokines, etc.
Plasma Fe, Zn
Plasma acute
phase proteins
Begin
Figure 18–20
Systemic responses to infection or injury (the acute phase response). Other cytokines probably also participate. This fi gure does not include all
the components of the acute phase response; for example, IL-1 and several other cytokines also stimulate the secretion of insulin and glucagon.
The effect of cortisol on the immune response is inhibitory; cortisol provides a negative feedback action to prevent excessive immune activity
(Chapter 11).
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