How did they do that? They conducted experiments which included pinealectomy along with rhythmic synchronisation. While the former is the procedure of removing the pineal gland, the latter analysis sees how your body works in the absence of melatonin.
The results helped the scientists conclude that there is a common functionality between the synthesis of melatonin and your immunity system.
Hence, now the question is, do you need to actually buy melatonin supplements and consume them? And, why is that?