In the previous Tetramer Tips blog, I suggested ways for you to be a negative Control Freak. Now it’s time to think positive! A positive control for a tetramer is a sample that contains cells expressing the specific T cell receptor of interest, i.e. has the exact specificity of the tetramer. Okay, brace yourselves; I’m going to be frank here. Having a positive control for tetramer experiments is often a quest for the Holy Grail. In many (most, in fact) cases, you will not have access to a positive control, unless one of your experimental samples happens to show a positive result. In an experiment where no positive events are seen and no positive control was used, you cannot necessarily conclude that the donor/patient/mouse is negative for that T cell specificity, because, heck, maybe you got distracted while pipetting and forgot to add the tetramer to your staining cocktail! A tetramer experiment with no positive control and no positives in the experimentals is, therefore, uninterpretable. This is the hard truth we must face.
Before you slip into despair about this, there are ways to obtain or create positive controls:
We researchers are trained and driven to control and predict, which is particularly handy for rare events flow cytometry with tetramers. Just remember to use these skills for good, not evil: when you go home at the end of the day, be sure to leave the Control Freak behind in the lab, planning the next experiment.