Cytokines: Chemical Mediators in the Immune System
1.
Cytokines are hormonelike chemical messengers secreted by lymphocytes and
macrophages that affect the immune response.
2.
Mediators affecting Lymphocytes
|
Cytokine |
Major
Source |
Important
Functions |
|
Interleukin-1 |
Macrophages |
Stimulates
growth of lymphocytes, neutrophils, epithelial cells and fibroblasts. Stimulates
helper T cells to differentiate and produce IL-2. Endogenous
pyrogen: acts on hypothalamus to cause fever. Inflammation
mediator. |
|
Interleukin-2 |
TH1
cells |
Stimulates
growth of both helper and cytotoxic T cells. Acts
synergistically with IL-4 to stimulate growth of B cells. |
|
Interleukin-4 |
TH2
cells |
Stimulates
B cell growth. Increase
isotype switching and IgE synthesis. Increase
number of TH2 cells. |
|
Interleukin-5 |
TH2
cells |
Stimulates
B cell differentiation. Enhances
synthesis of IgA. Stimulates
the production and activation of eosinophils. |
|
Interleukin-6 |
Helper
T cells |
Stimulate
B cell differentiation. |
|
Interleukin-10 |
TH2
cells |
Inhibits
development of TH1 cells by limiting interferon-g
production. |
|
Interleukin-12 |
Macrophages |
Promotes
development of TH1 cells by stimulating interferon-g
production. |
3.
Mediators affecting Macrophages and Monocytes
|
Cytokine |
Major
Source |
Important
Functions |
|
Chemotactic
factors: C5a, IL-8 |
Released
during inflammation |
Attracts
monocytes and macrophages to site of tissue injury and infection. |
|
Interferon-g |
TH1
cells |
Stimulates
phagocytosis and killing by macrophages. Increases
class I and II MHC expression. |
4.
Mediators affecting Polymorphonuclear Leukocytes
|
Cytokine |
Major
Source |
Important
Functions |
|
Chemotactic
factors: C5a, IL-8 |
Released
during inflammation |
Attracts
neutrophils, basophils, and eosinophils selectively to the site of injury
and inflammation. |
|
TNF-a |
Macrophages |
Low
concentration: activates neutrophils and increases their adhesion to
endothelial cells. |
5.
Mediators affecting Stem cells
|
Cytokine |
Major
Source |
Important
Functions |
|
IL-3 |
Helper
T cells |
Supports
the growth and differentiation of bone marrow stem cells. |
|
GM-CSF |
T
lymphocytes Macrophages |
Stimulates
the growth of granulocytes and macrophages. Enhances
the antimicrobial activity of macrophages. Used
clinically to improve regeneration of these cells after bone marrow
transplantation. |
|
G-CSF |
Macrophages Fibroblasts Endothelial
cells |
Enhances
the development of neutrophils from stem cells. Used
clinically to prevent infection in patents who have received cancer
chemotherapy. |
6.
Mediators with Other effects
|
Cytokine |
Major
Source |
Important
Functions |
|
Interferon-a |
Leukocytes |
Generates
antiviral and antiproliferative actions. |
|
Interferon-b |
Fibroblasts |
Generates
antiviral and antiproliferative actions. |
|
TNF-a |
Macrophages |
High
concentrations: important mediator of endotoxin-induced septic shock. Cachectin:
inhibits lipoprotein lipase in adipose tissue, reducing the utilization of
fatty acids. Causes
death and necrosis of certain tumors. |
|
TNF-b |
T
lymphocytes |
Stimulates
B cell proliferation. Generates
antiparasitic action (malaria, trypanosomiasis). Mediates
inflammatory reactions in endotoxic shock. |
|
Nitric
oxide |
Macrophages |
Vasodilation |