Defending Sperm Function

ß-defensins are a large family of cationic peptides with antimicrobial activities in vitro against Gram-positive and Gramnegative bacteria, fungi, and enveloped viruses [1]. As such, they are thought to be an important component of the innate immune system and are expressed by cells such as phagocytes and epithelia that are involved in host defence against microbial infections. The defensins form pores within the target membranes allowing the movement of small molecules across the plasma membrane and causing decreased bacterial viability. Several ß-defensins are expressed by epithelial cells of the caput epididymis where they may have a role in innate immunity of the urogenital system [2] or protecting sperm from immunorecognition [3]. To date, however, the exact role of ß-defensins in contributing to innate immunity in vivo has not been unequivocally established. It is possible that ß-defensins may have other important physiological functions beyond their antimicrobial activities. Indeed, a mutation in the Defb103 defensin gene causes a dominant black coat colour in dogs [4]. The paper in this issue of PLOS Genetics by Yu S. Zhou and colleagues contributes to our understanding of the function of ß-defensins in vivo by showing that they also have a role in sperm function [5]. To my knowledge, this is the first unequivocal demonstration of a ßdefensin phenotype in transgenic knockout mice.