I'm just trying to organize balanced panels to describe lymphocytes from my patients and I was wondering if its possible to detect autophagy with extracellular staining. I suppose Beclin 1, LC3 or Atg proteins can be only stained intracellulary.
I don't think that this approach is possible. There are many pitfalls when measuring autophagy rates. Please refer to established protocols. If you need more information please don't hesitate to contact me.
Please refer to the article below which has pretty much collect all methods studying autophagy. Enzo has a cyto-ID dye which I have not used but seems may work for your purpose.
Klionsky DJ, et al. Guidelines for the use and interpretation of assays for monitoring autophagy (3rd edition). Autophagy 2016; 12:1-222.