小中大
it's difficult for you to detect TNF-a in the supernatant using western blot. One reason is the concentration is lower. The other reason is the M.W of tnf-a is about 17kD, it's a little small to detect using western. I suggest you that the elisa is the first choice, it's sensitive to detect only 4 pmol of TNF, and it's also easy to do.