LL-37

Where it comes from

Made in

Neutrophils, and the keratinocytes of the skin and the cells lining the airways and gut

Sent out by

Infection and injury; vitamin D switches the gene on, one reason vitamin D matters to the defence against infection

Acts on

• Bacteria, fungi and enveloped viruses
• Immune cells
• Wound edges

What it does

• Kills a broad range of microbes
• Calls in immune cells and neutralises bacterial endotoxin
• Helps wounds close and new vessels grow

In medicine

• No approved medicine. In a 34-patient first-in-man trial, synthetic LL-37 on hard-to-heal venous leg ulcers sped healing at the two lower doses and did nothing at the highest ²
• Too much of it in the skin drives rosacea; too little, as in atopic dermatitis, invites infection ¹

Beyond the body’s own use

• OP-145, a peptide designed from LL-37, was tried as ear drops in long-standing middle ear infection: in a phase 2a trial of 34 adults, 47 per cent were counted a treatment success against 6 per cent on placebo ³
• Cathelicidin LL-37 is one of the peptides injected outside approved medicine. Reviewing it as a bulk substance for pharmacy compounding, the FDA said the safety information was insufficient, and pointed to a risk of immune reactions and, in animal work, to harm to male reproduction and tumour promotion in some tissues ⁴
• Unapproved and compounded preparations are not reviewed for safety, effectiveness or quality
• The gene is a direct target of the vitamin D receptor, so supplementation trials measure LL-37 as well as infections; that the peptide rises does not by itself show fewer infections ¹