To help differentiate between acute graft rejection and severe infection, Dharnidharka et al. performed a study on 29 children who received kidney transplant in 1 year of observation [97]; although the serum KYN/Trp ratio was significantly higher in those who experienced acute graft rejection, peripheral blood CD4-ATP levels were useful in differential diagnosis, because they were lower in the group with infections. This evidence concerns the gene ATP8A2 and infection.