Human beta-defensin 4

Where it comes from

Made in

Testis, epididymis, stomach, lung and skin, at low levels

Sent out by

Induced by bacteria in airway cells; much of it under conditions not yet known

Acts on

• Pseudomonas and staphylococci
• Yeast

What it does

• Kills bacteria and attracts monocytes
• One of over thirty beta-defensin genes, most of which guard the male tract
• Little studied beside hBD-1 to 3, and its job in people is not established

In medicine

• Nothing of its own. Its gene sits in the repeated block on chromosome 8 whose copy number varies and has been linked to psoriasis, but the link is to the block, not to hBD-4 ²
• No medicine, and nothing is measured through it in practice

Beyond the body’s own use

• Most of what is known comes from the paper that found it: the peptide is induced rather than made constantly, and its killing weakens as salt rises, the pattern of a surface defence rather than a circulating one ¹
• It is not in trials. The open question is whether the testis and epididymis, where it is most expressed, use it for defence at all ¹