0 -> Normal_Th_cells
Normal_Th_cells -> 0
Normal_Th_cells -> Single_Infected_Th_Cells
Single_Infected_Th_Cells -> 0
Single_Infected_Th_Cells -> Double_Infected_Th_Cells
0 -> Pathogen_Virus
Double_Infected_Th_Cells -> 0
0 -> Recombinant_Virus
Pathogen_Virus -> 0
Recombinant_Virus -> 0