Mean concentrations (±SEM) of tryptophan and kynurenine in serum of HIFM transplanted gnotobiotic pigs fed protein deficient diet (Deficient HIFM) and protein sufficient diet (Sufficient HIFM) groups. White arrows and a black arrow indicate time points for vaccination by oral attenuated HRV inoculation and virulent HRV challenge, respectively. Significant difference (*p < 0.05) between Deficient HIFM and Sufficient HIFM groups at each time point were determined by Mann-Whitney U test. HRV; human rotavirus, Deficient; protein deficient diet, Sufficient; protein sufficient diet, HIFM; human infant fecal microbiota, PTD; post transplantation day, PVD; post 1st (2nd) vaccination day and PCD; post challenge day.