At the euthanasia endpoint, only TR4 expressed elevated transcription of the IFN-γ gene compared to the other transmitter animals, while all except TR1 expressed only background levels of TNF-α mRNA (Figure 9A), confirming the observations from the infection experiment that ferrets infected with a moderate dose of M. tuberculosis express a generally low level of pro-inflammatory cytokines. The gene discussed is IFNG; the disease is infection.