In acne vulgaris, antimicrobial peptides (AMPs) could play a dual role; i.e., 
protective by acting against Propionibacterium acnes, pro-inflammatory by acting 
as signalling molecules. The cutaneous expression of 15 different AMPs was 
investigated in acne patients; furthermore, the impact of isotretinoin therapy 
on AMP expression was analysed in skin biopsies from 13 patients with acne 
vulgaris taken before, during and after a 6-month treatment cycle with 
isotretinoin using quantitative real-time polymerase chain reaction. Cutaneous 
expression of the AMPs cathelicidin, human β-defensin-2 (HBD-2), lactoferrin, 
lysozyme, psoriasin (S100A7), koebnerisin (S100A15), and RNase 7 was upregulated 
in untreated acne vulgaris, whereas α-defensin-1 (HNP-1) was downregulated 
compared to controls. While relative expression levels of cathelicidin, HBD-2, 
lactoferrin, psoriasin (S100A7), and koebnerisin (S100A15) decreased during 
isotretinoin treatment, only those of cathelicidin and koebnerisin returned to 
normal after 6 months of isotretinoin therapy. The increased expression of 
lysozyme and RNase 7 remained unaffected by isotretinoin treatment. The levels 
of granulysin, RANTES (CCL5), perforin, CXCL9, substance P, chromogranin B, and 
dermcidin were not regulated in untreated acne patients and isotretinoin had no 
effect on these AMPs. In conclusion, the expression of various AMPs is altered 
in acne vulgaris. Isotretinoin therapy normalizes the cutaneous production of 
distinct AMPs while the expression of others is still increased in healing acne. 
Considering the antimicrobial and pro-inflammatory role of AMPs, these molecules 
could serve as specific targets for acne therapy and maintenance of clinical 
remission.