To increase the signal for serotypes with low infectivity, several approaches can be utilized. (1) Time of incubation can be extended from 24 to 48 h. (2) Multiplicity of infections can be increased. However, make sure that luciferase signal is dose dependent and is not saturated. (3) For many serotypes, pretreatment of HEK293 cell with Compound C together with interleukin-6 and tumor necrosis factor alpha will additionally increase the luciferase readout. The gene discussed is TNF; the disease is infection.