Lympho-epithelial Kazal-type-related inhibitor (LEKTI) is the defective protein 
of the ichthyosiform condition Netherton syndrome (NS). Strongly expressed in 
the most differentiated epidermal layers, LEKTI is a serine protease inhibitor 
synthesized as three different high-molecular-weight precursors, which are 
rapidly processed into shorter fragments and secreted extracellularly. LEKTI 
polypeptides interact with several proteases to regulate skin barrier 
homeostasis as well as inflammatory and/or immunoallergic responses. Here, by 
combining antibody mapping, N-terminal sequencing, and site-specific 
mutagenesis, we defined the amino-acid sequence of most of the LEKTI 
polypeptides physiologically generated in human epidermis. We also identified 
three processing intermediates not described so far. Hence, a proteolytic 
cascade model for LEKTI activation is proposed. We then pinpointed the most 
effective fragments against the desquamation-related kallikreins (KLKs) and we 
proved that LEKTI is involved in stratum corneum shedding as some of its 
polypeptides inhibit the KLK-mediated proteolysis of desmoglein-1. Finally, we 
quantified the individual LEKTI fragments in the uppermost epidermis, showing 
that the ratios between LEKTI polypeptides and active KLK5 are compatible with a 
fine-tuned inhibition. These findings are relevant both to the understanding of 
skin homeostasis regulation and to the design of novel therapeutic strategies 
for NS.