I would suggest the CD107 assay; check out my Cytotherapy paper (Siegers, G.M. et al 2011) for the protocol. This assay will tell you if the cells are activated and degranulating. Cytotoxicity assays will tell you if the GDTs are killing the targets (meaning that they have recognized and been activated by them). If this is the case, then antibody blocking assays will help you determine which antigens or receptors are involved. 'hope that helps! And yes, Wendy would be an excellent resource for all things gamma delta, I am sure! Good luck!