In article <3ore5j$jhm at jhunix1.hcf.jhu.edu>, <Chris Thoburn> wrote:
[snip]>
>>>Perhaps it would be better to start with a more focused idea:
>>>>>> Why does the immune system even exist?
[snip.. snip]
>>Several points:
> 1) Parasitism does not mean death. An organism may well carry a parasite load
> and be perfectly able to survive.
Yes but this state of balance normally requires a functioning immune system.
2) I do not agree with you that the FUNCTION of immune systems is to protect
> an organism from 'undesirables'. I have always been bothered by this concept,
> finding no reason at all to beleive that the immune system 'protects' one from
> anything. It is true that it is far easier to envision oneself as separate
I find your reaSoning difficult to understand. Individuals of most higher
species studied who are born with or acquire a major immunodeficiency die
very quickly unless maintained in germ free environments. To say the immune
sytem is unnecessary seems quite a ridiculous statement.
> from the rest of the world (protected in a 'military' manner by the immune
> system as a whole); however, where is the line between 'self' and 'non-self'
> or 'undesireable' drawn. Obviuosly it must be an arbitrary discrimination:
> To chose ones 'skin' is insufficient since within one are many orgainisms your
> immune system recognizes as 'foreign', to chose ones 'genetic background' is
> also a poor choice since that doesn't really make you who you are 'self', and
> to chose organisms that replicate on their own as 'foreign' is also
> inadequate. I agree with you that modification of the reproductive capacity
> may be the safest chioce but I seriously doubt that 'thought' concerning later
> reproductive capacity ever enters the equation. The system exists, time
> passes, the system is different than when it started. Each component has
> acted based on its construction and the enviroment around it. I really don't
> think that the immune system has a clue what 'self' 'non-self' 'foreign'
> 'undesireable' or any other descriptors are.
Where I would start to agree with you in part is that the arguments about
self/non-self are ideas imposed upon the study of the immune system by
immunologists.
Much classical immunology is based upon experiments where tissues are
tranplanted from one animal to another or effector cells are asked to
descriminate in-vitro between self or non-self tissues infected with
virus etc. Clearly these situations are "artificial" and not generally
encountered as the immune system evolved. However that doesn't mean
to say we can't use the results from these studies to interpret the
normal role of the immune system.
Polly's thoughts in this area are to my mind well worth considering
because she is trying to indicate another way at looking at and
interpreting the data.
> 3) I'm not sure that evolution can not be 'directed' under certain
> circumstances. I think that perhaps many possible machanisms fall under the
> broad category of 'evolution' and that some can indeed be focused.
Evolution is not directed. Some succesful strategies survive with higher
probability. Some things, such as an immune system maight become so important
that they are almost always necessary for the survival of the individual!
[snip snip]
Mike Clark, mrc7 at cam.ac.ukhttp://www.path.cam.ac.uk/MikeClark/
--
o/ \\ // || ,_ o Dr. M.R. Clark, Division of Immunology
<\__,\\ // __o || / /\, Cambridge University, Dept. Pathology
"> || _`\<,_ // \\ \> | Tennis Court Rd., Cambridge CB2 1QP
` || (_)/ (_) // \\ \_ Tel. 01223 333705 Fax. 01223 333875
