Abstract

Antimicrobial peptides of the defensin class are found in many organisms, and most defensins in humans and other mammals belong to the alpha and beta subgroups. Alpha-defensins are major components of neutrophil granules, and in addition to antimicrobial activity are chemotactic for monocytes and T-cells. Beta-defensins are expressed in epithelia and display a wide variety of functions, including antimicrobial and chemotactic activity, as well as roles in pigmentation and the reproductive tract.

My own interest in defensins arises from the spectacular variation in the copy number of their genes: for example, at the beta-defensin gene cluster on chromosome 8, individuals with two copies are quite uncommon, and most individuals have between 3 and 6 copies per diploid genome. This variation, and even more diverse copy number variation in some alpha-defensin genes, is technically challenging to measure accurately, and begs a simple question that remains largely unresolved – does variation in gene copy number lead to variation in immune function?

I will focus my discussion on the difficulties of gene copy number measurement (and our solutions to those difficulties), established work on case-control association studies, and work we have initiated on more direct analysis of the relationship between gene copy number and alpha-defensin function.