Update and Review,avian peptides

The intricate world of avian biology reveals a sophisticated defense system, with antimicrobial peptides (AMPs) playing a pivotal role in protecting poultry from a myriad of threats. These naturally occurring molecules are short, often cationic, peptide-based molecules that exhibit potent antimicrobial and immunomodulatory activity, positioning them as crucial components of the avian innate immune system. Research into avian antimicrobial peptides has unveiled their significant potential, not only in understanding natural defense mechanisms but also in developing novel strategies to combat infectious diseases.

A key class of avian antimicrobial peptides are the \u03b2-defensins. These small cationic nonglycosylated peptides, typically ranging from 1 to 9 kDa, have been successfully isolated and purified from various avian species, including chicken, turkey, and ostrich, as well as from epithelial cells. For instance, \u03b2-defensins have been identified from the blood of these birds, highlighting their systemic presence. Beyond \u03b2-defensins, other AMPs like gallinacins in chickens, which are cationic antimicrobial peptides, are recognized as endogenous natural antibiotics. The avian egg itself is a testament to this protective prowess, as it provides antimicrobial protection through various mechanisms, including AMPs that are incorporated into the egg white by the hen. The ovodefensin is one such example found within the avian egg.

The efficacy of these peptides extends to a broad spectrum of pathogens. Studies have demonstrated that avian antimicrobial peptides possess potent, broad-spectrum antibacterial activities. Specific examples, such as CATH-1(6\u201326) and ABD1, have been identified as two of the most potent avian AMPs effective against both Gram-positive and Gram-negative bacteria. Furthermore, research has shown that avian peptides can significantly reduce the survival of challenging microorganisms like *Candida albicans* and *Salmonella enteriditis*. The peptide known as Gallin, a member of a new avian AMP family, has shown potent antimicrobial activity against *E. coli*, enhancing our understanding of avian immune strategies.

Beyond their direct antimicrobial effects, avian antimicrobial peptides also exhibit crucial immunomodulatory functions. This means they can actively influence and regulate the host's immune response, helping to manage inflammation and promote healing. For example, Avian HDPs, which encompasses a range of host defense peptides, have been shown to have both antimicrobial and immunomodulatory properties. This dual action is vital in combating infections, as it not only targets the pathogen but also helps to rebalance the host's immune system. The immunomodulatory effects of novel antimicrobial peptides like PeptAID AMPs on avian macrophages are an active area of research, aiming to harness these properties for therapeutic benefit. In some cases, these peptides can even attenuate inflammation, as demonstrated by the study on CATH-2, which inhibits APEC-induced inflammation via specific cellular pathways.

The application of antimicrobial peptides in the poultry industry is a rapidly evolving field, offering promising non-antibiotic tools to combat infectious diseases. The reliance on traditional antibiotics has raised concerns about antibiotic resistance, making the development of alternatives like AMPs a critical endeavor. Antimicrobial peptides can be utilized through various administration routes, including oral, intraperitoneal, and in ovo administration, to prevent infections from bacteria in poultry. This approach aligns with the One Health framework, recognizing the interconnectedness of human, animal, and environmental health. The potential for antimicrobial peptides to reduce pathogens like *Salmonella* in chickens highlights their significance in ensuring food safety and animal welfare.

Research continues to uncover the diversity and mechanisms of avian antimicrobial proteins and peptides. From those found in avian eggshell to avian heterophils (a type of white blood cell), these molecules represent a rich source of innate immunity. Five bactericidal peptides, including chicken and turkey heterophil peptides, were purified decades ago, underscoring the long-standing scientific interest in this area. The ongoing exploration of avian antimicrobial peptides promises to yield innovative solutions for disease prevention and control, contributing to a more sustainable and healthier future for both poultry and humans.