DEFB105A encodes defensin beta 105A, a cationic antimicrobial peptide belonging to the beta-defensin family characterized by six conserved cysteine residues forming disulfide bonds 1. The primary function of DEFB105A is antibacterial defense through direct microbicidal activity. Beta-defensins like DEFB105A exhibit broad-spectrum antimicrobial activity, though mechanisms vary by pathogen type 2. DEFB105A is expressed in epididymal epithelium where it contributes to innate immunity of the urogenital system 1. The disulfide bond array is essential for antimicrobial efficacy, with alterations significantly attenuating activity against Gram-positive bacteria 2. Beta-defensins demonstrate salt-dependent antimicrobial properties 1 and can modulate epithelial function beyond direct antimicrobial effects 3. Clinically, DEFB105A serves as a microsatellite instability marker in liquid biopsies for cancer screening and immunotherapy response monitoring 4. The peptide shows potential therapeutic applications as part of microbicide development strategies 5. While DEFB105A's specific mechanisms remain incompletely characterized, the broader defensin family demonstrates multifaceted roles in host defense and epithelial regulation.