PDCD1 and Menkes disease: The proportion of IFN-γ+ cells in PD-1− CD8+ T-cells in the spleens of chickens with MD was increased relative to that in the uninfected chickens; however, no difference was observed between the proportions of IFN-γ+ cells in PD-1+ CD8+ T-cells in the spleens of uninfected and infected chickens (Figure 2B,D).