cytokines & taxonomy ?

[Steve Hopkins]

>I was wondering why cytokines, and lymphokines for that matter, are not 
>usually considered as a functional part of cell-to-cell communication, at 
>least not in the textbooks I have used.  Is the distinction between 
>hormones and -kines merely taxonomic?  Or is there a different mechanism 
>for -kines, for instance no secondary messangers or specific receptors as 
>there are for hormones?

>AB DiBernardo
>University of Pennsylvania

I don't see any distinction, and they are considered a functional part of 
cell-cell communication, especiially in immunology (What textbooks are you 
reading?). Cytokines ARE hormones; just a sub-category. It's the definition of 
hormone that is more difficult (for discussion see introduction of V.C. 
Medevei's book 'A history of endocrinology' (1982), MTP press. ) The 
distinguishing feature of cytokines is that they maintain local tissue 
homeostasis and function of tissues, rather than systemic homeostsis and 
fnction of the organism, which is the primary role of endocrine (the other 
major category) hormones.  (Cytokines are also not produced by speciaised 
organs.) Of course the edges of this categorisation are blurred (e.g. IL-6, 
M-CSF,IGF, neurotrophins?,) since natural selection didn't follow any rules 
and, unfortunately, immunologists, endocrinologists and neuroscientists havn't 
communicated too well until recently, so there is some dispute about 
boundaries, but fits pretty well. (?)

Steve Hopkins
Manchester