The threat of antibiotic resistance has catalyzed the demand for novel antibiotic alternatives in veterinary and human medicine. In response, the activation of the innate immune system has become a promising alternative against resistant microbial infections.

Host defense peptides (HDPs) are immunomodulatory peptides innately produced by mucosal epithelial cells along the gastrointestinal, respiratory, and urogenital tracts. These small-chain peptides utilize their dual hydrophobic and hydrophilic regions and cationic charges to electrostatically interfere with protein and nucleic acid synthesis in bacteria, fungi, protozoa, and cancer cells. HDPs recruit neutrophils, monocytes, and reduce the proinflammatory response, making them key modulators to the innate immune system.

This study analyzes the potential for two epigenetic modulators, S-adenosylhomocysteine (SAH) and all-trans retinoic acid (ATRA), to induce HDP synthesis in chicken macrophage cell lines (HTC). It was hypothesized that SAH and ATRA would upregulate HDP gene expression independently and in combination with butyrate, a short-chain fatty acid known to induce HDPs.

Independent trials were conducted to determine the ideal 24-hour treatment dosage of SAH and ATRA for HTC cells. Additionally, combination trials were conducted to analyze the synergy between each modulator and butyrate. Following treatment, RNA was isolated, subjected to reverse transcription, and gene expression was quantified by analyzing AvBD9 expression, a known avian HDP, normalized against GAPDH.

Current results suggest that SAH and ATRA induce AvBD9 expression at optimal concentrations of 10 _M and 1 _M, respectively. However, neither compound induces statistically significant HDP expression independently or in synergy with butyrate. Further studies will be continued to confirm ATRA and SAH concentrations and avian HDP response.