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 109 is an 87 amino acid secreted protein that is notably expressed on the ocular surface and is found in reduced levels in microbial infection, therefore suggesting that this particular Beta-defensin is unlikely to have a major antimicrobial effect.