The gene expression of both the first rate-limiting Tph1 and Ddc enzymes of 5-HT synthesis, known to correlate with 5-HT production in the lung12, were increased early in infection in Tph1+/+ mice and followed later on by the increased expression of the genes Aanat and Maoa, encoding for 5-HT degradation to N-acetyl-hydroxytryptamine (NAS) and 5‐OH-IAA21,32, respectively, but not of the Asmt gene encoding for melatonin production (Fig. 3b). Here, DDC is linked to infection.