Growth hormone (GH), prolactin (PRL), and the neurohypophysial arginine vasopressin (AVP) are immunomodulators/immunostimulators [4], [14]–[21], whereas sex hormones of the hypothalamic-pituitary-gonadal (HPG) axis affect the susceptibility of the immune system when facing immune challenges, thus determining the development of infections and autoimmune diseases [22]. This evidence concerns the gene PRL and infection.