2
Expressing a protein means that the protein is produced in those cells at a detectable level.
From https://www.merriam-webster.com/dictionary/express
: to cause (a gene) to manifest its effects in the phenotype
also : to manifest or produce (a character, molecule, or effect) by a genetic process
This is basic biology terminology. I'd highly recommend ...
Only top voted, non community-wiki answers of a minimum length are eligible