You may find this site worth reading
http://www.vet.cornell.edu/fhc/resources/brochure/toxo.html
and this one
http://www.fabcats.org/toxoplasmosis.html
I think when they are talking about immune supression they mean co-infection with feline leukemia virus (FeLV) or feline immunodeficiency virus (FIV) not just being otherwise ill.
If you get the liver situation under control he should begin eating better.
I think any eating is a good sign when dealing with the liver problem especially when you are also using a feeding tube.
If you aren't treating for the toxoplasmosis you might ask your vet about antibiotics and if the liver can handle them.
Hope this helps you!
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