A Ca2+ concentration of 1.5 mM, as present in IMDM but not in RPMI, is critical for maximal response of Th cells to PMA/ionomycin

Restimulation of memory–effector T helper lymphocytes with PMA/ionomycin is an established technique to determine their imprinting for the expression of cytokine genes, that is their functional potential. Here, we show that for the maximal reexpression of cytokine genes, the Ca2+ concentration of the medium has to be greater than 1.5 mM. For RPMI (Roswell Park Memorial Institute 1640), the most commonly used medium, the Ca2+ concentration has to be increased from the regular 0.42 to 1.5 mM.