Download Cytokines and Chemokines

Cytokines and Chemokines
• Cytokine or immunocytokine is a generic name used to describe
a diverse group of soluble proteins and peptides which act as
humoral regulators at nano- to- picomolar concentrations
• Cytokines modulate the functional activities of individual cells
and tissues both under normal and pathologic conditions
• Interleukins - produced exclusively by leukocytes
• Lymphokines - produced by lymphocytes
• Monokines - produced exclusively by monocytes
• Interferons - involved in antiviral responses
• Colony Stimulating Factors - support the growth of cells in
semisolid medias
• Chemokines
• The term cytokine is used to separate this group of
immunomodulatory proteins from other growth factors that
modulate non-immune cells
• Unfortunately, Growth factors and cytokines both act as cellular
survival factors by preventing apoptosis - this fact adds
confusion to the understanding and naming of cytCytokines
behave like classical hormones in that they act at a systemic
level, affecting, inflammation, septic shock, acute phase
reactions, wound healing, and the neuroimmune network
• Unlike hormones, cytokines are not produced by specialized
cells or in specialized glands - they have no single organ source
(this helps clear some of the confusion
• okines
• Cytokine actions may be characterized as:
• Autocrine (self modulating)
• Paracrine (modulating cells in the immediate surroundings)
•
• Almost all Cytokines are pleiotropic effectors showing multiple
biological activities
• Also, multiple cytokines often have overlapping activities
• A single cell frequently interacts with multiple cytokines with
seemingly identical responses - cross-talk
• Many Membrane-bound cytokine forms have been characterized
• Some cytokines may also be associated with the extracellular
matrix
• Switching between soluble and membrane bound forms of
cytokines may be an important immunoregulatory event
• Most Cytokines are not stored inside cells (exceptions are, for
example TGF-b and PDGF which are stored in platelets)
• The expression of most Cytokines is strictly regulated - factors
are usually produced only by activated cells in response to an
induction signal
• Expression is normally transient and can be regulated at all
levels of gene expression
• Cytokine mediators can be transported quickly to remote areas
of a multicellular organism
• They can address multiple target cells and can be degraded
quickly. Concentration gradients can be used to elicit specific
responses
• Cytokines are important mediators involved in embryogenesis
and organ development and their activities in these processes
may differ from those observed postnatally
• They also play a key role in neuroimmunological,
neuroendocrinological, and neuroregulatory processes
Regulation
Cytokines are important positive or negative regulators of mitosis,
differentiation, migration,cell survival, apoptosis, and transformationoncogene
Viral effects
• Viral infectious agents exploit the cytokine repertoire to evade
immune responses of the host
• Virus-encoded factors appear to affect the activities of cytokines
in at least four different ways:
– by inhibiting the synthesis and release of cytokines from
infected cells
– by interfering with the interaction between cytokines and
their receptors
• Virus-encoded factors appear to affect the activities of cytokines
in at least four different ways:
– by inhibiting signal transmission pathways of cytokines
– by synthesizing virus-encoded cytokines that antagonize
the effects of host cytokines mediating antiviral processes
(viroceptor and virokines)