Introduction
Antimicrobial peptides (AMP)Generally speaking surfaces like the skin or the oral mucosa are protected by several factors including the adaptive and innate immune systems against invading bacteria and fungi. The antimicrobial mucosal shield of the human airways has been subject of several studies and is well investigated [1][2][3]. A growing number of different human antimicrobial peptides (AMP) have been described which are produced e. g. by surface epithelial cells or by neutrophil granulocytes. The AMPs have a broad, but not identical spectrum of antimicrobial activity against bacteria, virus or fungi. A synergistic and additive effect of different AMPs has been reported [4]. In addition to their antimicrobial charactics, AMPs play a major part in inflammation, immune activation, and wound healing [5][6][7]. Some of the well described AMPs are subject to this study and therefore will be further described.
The human ß-Defensins (hBD)The family of human ß-Defensins (hBD) is named after their beta-sheet structure which is stabilised by intramolecular disulfide bonds. Human ß-Defensin 1 (hBD1) was first isolated from hemofiltrate [8] and is expressed in epithelial cells of the urinary, respiratory tract and in keratinocytes [9][10]. It has a strong antimicrobial effect on Gram-negative bacteria [11][12]. Human ß-Defensin 2 (hBD2) is an inducible (by Escherichia coli, Pseudomonas aeruginosa, Helicobacter pylori, Lipoprotienacid, Candida albicans, TumorNecrosis-Factor-α, Interleucine1-ß) peptide [13][14][15] with a strong antimicrobial effect on Escherichia coli, Pseudomonas aeruginosa and Candida albicans, and a relatively weak effect on Staphylococcus aureus [13]. The human ß-Defensin 3 (hBD3) can be induced by tumor necrosis factor α and contact with Pseudmonas aeruginosa or Staphalyococcus aureus e. g. in keratinocytes [16]. HBD3 has antimicrobial activity against Staphylococcus aureus, including Methicillin restistant Staphylococcus aureus (MRSA), Streptococcus pyogenes, Pseudomonas aeruginosa, Escherichia coli, Vancomycin-resistant Enterococcus faecium, Candida albicans and Haemophilus influenza [9; 12; 17].
Human LL-37 (LL-37)LL-37 is the 37-amino acid long C-terminus and the antimicrobial active component of the human Cathelicidin antimicrobial peptide 18 (hCAP-18). It is expressed in leukocytes (monocytes, neutrophiles, T-cells, B-cells), epithelial cells (skin, gastrointestinal and respiratory tract) and secreted into wound and airway surface fluid [18][19][20][21]. LL-37 alone and in combination with other AMPs is bactericidal against a broad spectrum of [21][22][23]. Apart from the antimicrobial activity LL-37 plays a role in angiogenesis, cancer development, neutralisation of bacterial lipopolysaccharide and is chemotactic for human monocytes, neutrophils and CD 4 T-lymphocytes [24-26.].
Human Secretory Leucoprotease Inhibitor (hSLPI)hSLPI is a 11.7-kDa heavy protein which is expressed in macrophages, neutrophils and epithelial cells [27-28.].The antimicrobial activity against Gram-negativ...