what's the passage of cell?

[maryli]

I wonder the exact definition of 'passage of cell'. Somebody told me when I trypsinized cells, I should add one passage. Other man told me if one cell divided into 2, it will be the 2nd passage. can you give me your opinion? Thanks a lot.

[blcr11]

Passage number refers to the number of times the cell line has been re-plated and allowed to grow back to confluency (or to some maximum density if you're using suspension cultures). Each time you trypsinize an adherent cell line to replate it, you add 1 to the passage number. The higher the passage number, the farther away you must be from the primary explant--or whatever--the cell line was derived from. This will be most important for those times when you're establishing a cell line from a primary source (a fresh tumor or fresh piece of tissue or fresh batch of lymphocytes, etc) or else you need to keep track of the number of passages of the primary to secondary growths to be sure you don't lose whatever properties you are trying to study.

[maryli]

thanks for your kind reply.