Re: What are cytokines, and how do they work?

What are cytokines and how do they work?
Cytokines are a group of mostly soluble molecules (peptides and proteins) 
that mediate cell to cell communication and show their physiological effect 
in nano- to picomolar concentrations (which is very low). They comprise 
interleukins, chemokines, and other molecules such as growth factors. 
   They can act as signals between all the different blood/immune cells 
(where they were first described in the 1960s), between nerve cells and 
blood/immune cells, and vice versa. Basically all cells that are involved 
in an immune response in some way or other (or the ones derived from blood 
cell precursors) will react to cytokines which in this case function as 
immune modulators and growth factors.
Other cell types such as nerve cells, endothelial cells (the ones lining 
blood vessels), kidney cells, placental cells, etc., respond to cytokines 
as well. 

Cytokines are no homogeneous group of molecules but are grouped together 
because of their functional similarity. They can be subdivided into 
families based on structural similarities, e.g. the IL-1 family, the 
IL-6/LIF/oncostatin family, etc. 

Cytokines are involved in
a)  development, e.g. as so called hematopoietic factors that control the     
    development of blood cell precursors into different kinds of blood and 
    immune cells
b)  inflammation, e.g. pariodontitis (inflamed gums), allergies, autoimmune     
    diseases, etc.
c)  physiological stress, e.g. in wound healing, fever, etc.
d)  other processes and ailments/diseases: osteoporosis and control of bone     
    physiology in general, depression and other psychiatric disorders,     
    anorexia, some disorders of the heart (not in love sickness though I am         
    afraid)

Cytokines work by specifically binding to their receptors which 
themselves can be subdivided into various families. Most receptors are 
multimers, i.e. they consist of two or more subunits (either identical or 
nonidentical), and some may require coreceptors to function. 
Upon binding the cytokine activates the receptor, and subsequently one of a 
number of signal transduction pathways is turned on, which eventually leads 
to a change in gene expression.


References (there are tons of them dealing with the roles of cytokines in 
specific disorders or physiological processes but I selected some more 
general ones):
1. Curfs JH, Meis JF, Hoogkamp-Korstanje JA (1997). A primer on 
   cytokines: sources, receptors, effects, and inducers. Clinical 
   Microbiology Reviews 10(4):742-80
2. Holtmann H and Resch K (1995). Cytokines. Naturwissenschaften 82: 
   178 - 187.
3. Rosenbaum JT, Brito B, Han YB, Park J, Planck SR (1998). 
   Cytokines. An overview. Advances in  Experimental Medicine and Biology 
   438:441-6

Some selected online references:

The Cytokine Homepage
The Cytokine Web

ABC News article on chronic pain in cancer and the possible role of 
cytokines
 

I hope this answers your question. In case you have any more questions feel 
free to email me