We report the isolation and characterization of a novel peptide with significant sequence homology to 0-defensins from human blood filtrate. The human 0-defensin-I (hBD-I) is a short basic peptide of 36 amino acid residues. It contains six cysteines forming three intramolecular disulfide bonds. The molecular mass of hBD-1 is 3928.6 Da. Cloning of the specific cDNA confirmed the amino acid sequence of the native peptide, hBD-1 shares the nine conserved amino acids characteristic for ~B-defensins from respiratory epithelial cells and neutrophils of cattle and chicken leukocytes, hBD-1 is present in nanomolar concentration in human plasma.

Proteinase inhibitors are important negative regulators of proteinase action in vivo. We have succeeded in isolating two previously unknown polypeptides (HF6478 and HF7665) from human blood filtrate that are parts of a larger precursor protein containing two typical Kazaltype serine proteinase inhibitor motifs. The entire precursor protein, as deduced from the nucleotide sequence of the cloned cDNA, exhibits 15 potential inhibitory domains, including the Kazal-type domains, HF6478, HF7665, and 11 additional similar domains. An inhibitory effect of HF7665 on trypsin activity is demonstrated. Because all of the 13 HF6478-and HF7665-related domains share partial homology to the typical Kazal-type domain but lack one of the three conserved disulfide bonds, they may represent a novel type of serine proteinase inhibitor. The gene encoding the multidomain proteinase inhibitor, which we have termed LEKTI, was localized on human chromosome 5q31-32. As shown by reverse transcriptase-polymerase chain reaction and Northern blot analysis, it is expressed in the thymus, vaginal epithelium, Bartholin's glands, oral mucosa, tonsils, and the parathyroid glands. From these results, we assume that LEKTI may play a role in antiinflammatory and/or antimicrobial protection of mucous epithelia.Proteinases are enzymes required for nonspecific processes of digestion and intracellular protein turnover as well as specific proteolytic activation of inactive precursors of many regulatory proteins, such as enzymes and peptide hormones. In addition, they are involved in several processes of extracellular matrix remodeling. Depending on the nature of their reactive center, they are subdivided into the classes of serine, cysteine, aspartate, and metalloproteinases (for review see Ref. 1). To control the action of proteinases in vivo, organisms produce another group of proteins, namely the proteinase inhibitors (for review see Refs. 2-4). Indeed, many pathological effects are due to the non-regulated action of endogenously produced proteinases or such proteinases encoded or synthesized by viruses, bacteria, and parasites (for review see Ref. 5). For instance, a genetically determined fault of the ␣ 1 -proteinase inhibitor may lead to an enhanced proneness to lung emphysema caused by uncontrolled action of leukocyte elastase (6 -8). Thus, proteinase inhibitors represent an important therapeutic tool for a large number of different disorders.Here we report the isolation of two peptides (HF6478 and HF7665) from human blood filtrate (hemofiltrate), which may represent a novel class of proteinase inhibitor. Blood filtrate, a by-product of ultrafiltration of the blood from patients with acute renal failure, is routinely used by us as a source for the systematic as well as random isolation of novel human peptides (9). Due to the cut-off limit of the hemofilters (approximately 20,000 Da), it mainly contains peptides exhibiting a molecular mass below 20,000 Da. Nevertheless, we succeeded in isolating members of many different peptide/protein families suc...

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The inhibition of hK5 and hK7 by LEKTI domain 6 indicates an important regulatory role of LEKTI in processes of skin desquamation and inflammation, which may explain the severe pathological symptoms associated with abnormalities of SPINK5 and/or its expression. Thus, LEKTI represents a potential drug for the treatment of these disorders.