The nervous system and innate immunity: the neuropeptide connection.

Many neuropeptides and peptide hormones are very similar to antimicrobial peptides in their amino acid composition, amphipathic design, cationic charge and size. Their antimicrobial activities suggest they may also be directly involved in innate defense. Here we discuss recent advances in understanding how the mammalian nervous system, equipped with neuropeptides and peptide hormones with potent antimicrobial properties, might directly defend the host from microbial assault. As examples, we have chosen five well described, locally produced neuropeptides that may serve a previously unrecognized, direct antimicrobial, innate immune function in four anatomical sites.