There are many ways of stimulating cells polyclonal. It is also the most
often used way of stimulation to do intracellular staining. You can think of
the already mentioned PMA/ionomycin stimulation which activates almost any
cell to produce any protein it can. This is also the most unphysiologic way of
stimulation. You can also think of CD3/CD28 or lectin (PHA or ConA)
stimulation of T cells or LPS stimulation of monocytes or keratinocytes.
Specific, monoclonal stimulation
This is the most physiologic way of stimulation. And you can think of the
percentage antigen specific T or B lymphocytes in your PBMC. That way you got a
screening method for changes due to immunization protocols i.e.