Can you tell me which kind of tissue you are using as positive control. We
have the same antibody in our lab (antiCD4 from Novocastra) and experience
the same problem. Up to now no staining was obtainable on specimens of
patients with chronic inflammation of the gut (even with different
pretreatment protocolls, MW, Cooking using 1mM EDTA etc). In the Novocastra
catalogue they show an example of CD4 positivity on human skin, mycosis
fungoides (a rare T cell lymphoma to my knowledge). In my opinion I think
that you have to apply extreme amounts of antibody (recommended dilution in
the range of 1:20 to 1:40.
If your tech was able to stain in the other lab maybe you can get tissue
samples from this lab as well as an aliquot of the antibody (maybe a
different lot number helps) they use over there. Retest it in your lab.
If you make new experiences please let us know.

Best regards.

Michael

Michael Stumm, MD, Lab 405
Department of Research
Kantonsspital Basel
Hebelstrasse 20
4031 Basel
Switzerland
phone: ++41/61/265 23 84
email: stumm@ubaclu.unibas.ch