DEFB104A encodes human beta-defensin-4 (HBD-4), an antimicrobial peptide with dual roles in innate immunity and immune cell recruitment. Primary function: HBD-4 contributes to defense against both Gram-positive and Gram-negative bacteria through direct antimicrobial activity and serves as a chemoattractant for monocytes 1. Mechanism: HBD-4 functions as an inducible antimicrobial peptide, with expression regulated by inflammatory signals such as phorbol esters. The peptide exerts bactericidal effects, though expression levels in gastric tissue are typically minimal under basal conditions 1. Disease relevance: DEFB104A copy number variation (CNV) represents a genetic polymorphism associated with susceptibility to infections. CNV in DEFB104A, alongside DEFB4 and DEFB103A, has been investigated as a potential genetic factor affecting HIV infection risk and disease progression 2. The copy number status varies among populations, demonstrating population-specific genetic diversity 2. Clinical significance: Reliable quantification of DEFB104A copy numbers requires multiplex ligation-dependent probe amplification rather than real-time PCR, which has higher variability 3. Understanding DEFB104A genetic variation may inform personalized assessments of innate immune competence and infectious disease susceptibility, though further validation studies are needed 2.