IDO1 and systemic sclerosis: Finally, post hoc comparisons using the Bonferroni t-test correction indicated that male SSc patients had: (1) lower TRP concentrations than male HC (MD = −8767.50; p = 0.001; 95%CI [−13541.948; −3993.059]), (2) higher KYN concentrations than male HC (MD = 1942.713; p < 0.001; 95%CI [1058.594; 2826.832]), (3) higher IDO and TDO activity than male HC (MD = 0.095; p < 0.001; 95%CI [0.068; 0.122]), (4) lower KAT activity than male HC (MD = −0.006; p = 0.004; 95%CI [−0.010; −0.002]), and (5) higher KYNA/TRP ratio than male HC (MD = 0.001; p = 0.015; 95%CI [8.502 × 10−5; 0.001]).