"Pustulosis palmaris et plantaris", or palmoplantar pustulosis (PPP), is a 
chronic pustular dermatitis characterized by intraepidermal palmoplantar 
pustules. Although early stage vesicles (preceding the pustular phase) formed in 
the acrosyringium contain the antimicrobial peptides cathelicidin 
(hCAP-18/LL-37) and dermcidin, the details of hCAP-18/LL-37 expression in such 
vesicles remain unclear. The principal aim of the present study was to clarify 
the manner of hCAP-18/LL-37 expression in PPP vesicles and to determine whether 
this material contributed to subsequent inflammation of lesional skin. PPP 
vesicle fluid (PPP-VF) induced the expression of mRNAs encoding IL-17C, IL-8, 
IL-1α, and IL-1β in living skin equivalents, but the level of only IL-8 mRNA 
decreased significantly upon stimulation of PPP vesicle with depletion of 
endogenous hCAP-18/LL-37 by affinity chromatography (dep-PPP-VF). 
Semi-quantitative dot-blot analysis revealed higher concentrations of 
hCAP-18/LL-37 in PPP-VF compared to healthy sweat (2.87±0.93 µM vs. 0.09±0.09 
µM). This concentration of hCAP-18/LL-37 in PPP-VF could upregulate expression 
of IL-17C, IL-8, IL-1α, and IL-1β at both the mRNA and protein levels. 
Recombinant hCAP-18 was incubated with dep-PPP-VF. Proteinase 3, which converts 
hCAP-18 to the active form (LL-37), was present in PPP-VF. Histopathological and 
immunohistochemical examination revealed that early stage vesicles contained 
many mononuclear cells but no polymorphonuclear cells, and the mononuclear cells 
were CD68-positive. The epidermis surrounding the vesicle expresses monocyte 
chemotactic chemokine, CCL2. In conclusion, PPP-VF contains the proteinase 
required for LL-37 processing and also may directly upregulate IL-8 in lesional 
keratinocytes, in turn contributing to the subsequent inflammation of PPP 
lesional skin.