Even though TCR-γ is a co-receptor of CD8 and CD4 in cytotoxic and helper lymphocytes, it seems to be up-regulated upon infection with the mutant low-virulent strain (especially 3 dpi) without simultaneous up-regulation of CD8 and CD4, suggesting that T-cells are not present in the target tissue at that time point [6]. The gene discussed is CD4; the disease is infection.