IFNG and infection: It has to be kept in mind though that a comparison of IFN-γ SCs between different studies has to be done with caution as results are influenced by inter-assay variability caused by differences in restimulation time, MOI, type of antigen used for restimulation, the particular PRRSV strain used for infection and re-stimulation, as well as the immune status and the age of the pig [37].