Following earlier discussions re: Caltag and, perhaps, tying in to the more recent TdT neg ALL exchanges we also had an apparently negative T-ALL (2/cy3/5/7/8/34) the other day. I say apparent because a repeat of the staining using our in house method gave a clear (admittedly dim) TdT positive result where the HT6 clone in Fix & Perm was unequivocally (0%) negative.Both methods were whole blood using identical concentrations & timings. The strength of the cytoplasmic CD3 staining was the same by both techniques so it appears that the nuclear membrane may be a little too tough for An der Grubb's stuff. As I said way back when, I have always been suspicious of the strength of Caltag TdT staining but I didn't expect such a big disagreement between methods. In future all our TdT staining (tho' not MPO!) will be by our own method - we just have to sort out the higher autofluorescence seen with AML's after fixation (must re-read the postings on this). Since I'm on about TdT, what do other contributors feel about setting the positive region ? Matched isotypic, unstained control, TdT staining on normal lymphs or what ? Wal Sharp SQU Oman
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