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The overuse of antibiotics for more than 50 years has led to the resistance of bacteria to most of them. The problem is not only the accumulation of mutations in bacterial genome over time, but also the absence of new classes of antibiotics in recent years. The current strategy to overcome the resistance of bacteria to antibiotics is, among others, using antimicrobial proteins and peptides that are produced by insects, amphibians, mammalians, or bacteria. One of the most interesting and promising group of peptides to use in the future in human and animal therapy are cationic peptides with β-sheet structures which are stabilised by cystein, called defensins. They are wide spread in the organisms of animals and plants. The mammalian defensins can be divided into three main classes: α-, β-, and Θ-defensin. The biggest is the class of β-defensins. They were discovered at the beginning of nineties of the last century. They demonstrate a broad-spectrum of cytotoxic activity and activity against bacteria and viruses. Their expression was found in many tissues of humans and animals. At present four human epithelial β-defensins, sixteen bovine, two ovine, two caprine, one porcine, four chicken, and four turkey β-defensins are known. Initially, only antibacterial, antiviral, and antifungal activities were attributed to these peptides. Nowadays, these peptides are known as multifunctional molecules. The type of their biological activity often depends on their concentration. Some of them are potential candidates for clinical applications and therefore the recognition of every aspect of their biological activity can be very important.
Hundreds of antimicrobial peptides (AMP) have been described in vertebrates, invertebrates, plants and even fungi. The present article describes the cathelicidins and defensins of pigs. Antimicrobial peptides possess direct antimicrobial activity against a wild spectrum of microorganisms (bacteria, fungi, viruses ect.) and the ability to modulate immunological response. The activity of AMP consists mainly in disrupting the microbial membrane. Defensins and cathelicidins are two main classes of AMP. To date, several AMP have been isolated from porcine tissues. The presence of AMP was confirmed in the bone marrow, tongue, trachea, kidneys, reproductive tract, urinary tract and small intestine. Porcine cathelicidins are the first cathelicidins isolated from mammals. So far, eleven porcine cathelicidins have been described: PR-39 (proline-rich 39-amino-acid peptide), PF-1 (proline-phenylalanine-rich prophenin-1), PF-2, cysteine-rich proteins called protegrins (PG) (from PG-1 to PG-5), three porcine myeloid antimicrobial peptides PMAP-23, PMAP-36 and PMAP-37. As yet, no á-defensins have been found in pigs; however, thirteen isoforms of porcine â-defensins (pBD) have been identified, including pBD-1, -2, -3, -4, -104, -108, -114, -123, -125, -126, -129 and pEP2C and pEP2E. In recent years, when the increasing bacterial resistance to antimicrobial agents has been observed, the studies of AMP are necessary, especially with respect to their role as an alternative to antibiotics.
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