GFP transduced cells and intracellular cytokines

Dear Flowers,

I have a querry similar to one asked recently by Ken McDonald. We have been using cells transduced with retroviral vector containing transgene for a fusion protein: preTNF-LINKER (23 aa)-EGFP. The cells are intensively green but we can not detect any TNFa (neither intracellular nor membrane bound). We use a BD anti-TNFa PE mAB at.no.340512 (clone 6401.1111) which suppose to stain both forms of TNF.
Any uggestions would be appreciated.
Jarek Baran,Ph.D.

Department of Clinical Immunology
Polish-American Institute of Pediatrics
Jagiellonian University Medical College
Cracow, Poland