Yes, for the IL-6 cytokine measurement. Remaining cell culture supernatant may be frozen at -20°C or -80°C for future use, e.g. retesting. Storage time of the frozen supernatant may be also dependent on the test substance used for stimulation of monocytes and needs to be individually determined by the user.
Please not that pro-inflammatory cytokines other than IL-6 cytokines, e. g. IL-1 beta cytokines are not stable upon freezing.