THI is a trace component present in the industrially produced food colorant caramel color III. It acts as an immunosuppressant by inhibiting the enzyme sphingosine 1-phosphate lyase (S1PL) which fragments S1P to hexadecenal and phosphoethanolamine. Administration of THI in drinking water to mice (50 μg/mL) resulted in decreased S1PL activity, increased S1P levels in lymphoid tissues and reduced egress of CD4+ and CD8+ T cells (lymphopenia).
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