UPP1 and infection: Most importantly, Toxoplasma gondii KU80 has been used to delete the orotidine-5′-monophosphate decarboxylase (OMPDC) and uridine phosphorylase (UP) genes to obtain an avirulent non-reverting pyrimidine auxotroph strain, providing novel tools for the dissection of the host Th1 immune response with respect to infection [34].