The myeloid a-/hdefensins and the enteric HD5 have also been reported to have inhibitory potential against enveloped and non-enveloped viruses, such as the herpes simplex virus, the human immunodeficiency virus, papillomaviruses, adenoviruses, polyomaviruses,Notoginsenoside-Fe the SARS coronavirus, influenza viruses and others. In addition to its role in host defense, HD5 also has a homeostatic role in establishing and maintaining the intestinal microbiota. Overall, these experimental studies indicate that the variable antimicrobial abilities of mammalian a-/ h-defensins compose an antimicrobial spectrum. Defensins with continuously shifting antimicrobial activity, together with other versatile antimicrobial factors, evolve to act as the first line of defense of the innate immune system and play important roles in the early host defense. Because of the therapeutic potential of antimicrobial peptides,Panaxadiol synthetic defensins are being developed as peptide drugs, such as the fusion inhibitors. Exploring the natural defensin repertories, especially in species closely related to humans, will help us understand the stability and plasticity of a-/h-defensins and aid in designing potent peptide drugs. The sliding window analysis of DEFT suggests that fragment 41–50 in the prosegment and fragment 66–75 in the mature peptide are under positive selection. These two fragments contain the positively selected sites detected by PAML. Other amino acid changes that may contribute to the high Ka/Ks value are 41G/E, 45S/A and 48R/W in fragment 41–50 as well as 69R/L, 71V/I/F and 73R/Q in fragment 66–75. To be spliced into an 18-residue mature h-defensin, the three C-terminal residues must be removed during the maturation process. The three C-terminal residues were not found to be under positive selection using the PAML software. However, the three C-terminal residues of h-defensin show a pattern of RLL or QLL that is quite different from the a-defensins, which might be related to their involvement in the maturation process of h-defensins. Multigene families play important roles in the immune system, the sensory system, development and other processes. These families can express gene products at high levels, such as highly conserved histones and nuclear ribosomal RNAs, and produce proteins with diverse functional spectra, such as a-defensins, major histocompatibility complex proteins, immunoglobulins, chemoreceptors and olfactory receptors.