Beta-defensins are small cationic peptides with broad-spectrum antimicrobial activity against a variety of enveloped viruses, fungi and bacteria. Produced in mucosal epithelia and neutrophils of several species, Beta-defensins are developmentally regulated. The family of Beta-defensin proteins share a common defensin-motif that is characterized by multiple cysteine residues and a highly conserved tertiary structure. Besides playing a significant role in host immune defense, many Beta-defensins also are involved in sperm maturation and capacitation. Beta-defensin 133 is a 61 amino acid secreted protein that has antibacterial activity.