Immunomodulatory activities of bovine host defense peptides (HDPs): context-dependent roles in inflammation and immune priming.

BACKGROUND: Maintaining immune homeostasis is essential for livestock health and productivity, particularly in the face of infection or stress. Host defense peptides (HDPs), including β-defensins and cathelicidins, are key innate immune components with both antimicrobial and immunomodulatory properties. This study aimed to characterize the immunomodulatory effects of five bovine HDPs-BNBD1, BNBD3, LAP, Bac5, and BMAP27-on peripheral blood mononuclear cells (PBMCs) and bovine turbinate (BT) epithelial cells, under both basal and lipopolysaccharide (LPS)-stimulated inflammatory conditions. Cytokine secretion, cell viability, and real-time epithelial cell behavior were assessed to evaluate peptide-specific immune modulation. RESULTS: Under non-stimulated conditions, LAP stimulated the secretion of IL-8 (LAP p < 0.0001). In LPS-stimulated PBMCs, prophylactic HDP treatment (4 h pre-LPS) amplified inflammatory cytokine secretion. BNBD3 and LAP significantly increased IL-1β, IL-6, TNF-α, IFN-γ (p < 0.05), and chemokines such as IL-8 and MIP-1α (p < 0.01), suggesting an immune-priming effect that may enhance responsiveness to subsequent LPS stimulation. Notably, BNBD3 and LAP failed to induce a comparable inflammation when added 0.5 h after LPS, highlighting the context-dependent nature of HDP action. Conversely, BMAP27 demonstrated anti-inflammatory activity by reducing LPS-induced IL-1β, IFN-γ, and IL-10 (p < 0.001), irrespective of timing. Bac5 increased IL-8 secretion (p < 0.001) and MCP-1 (p < 0.05), suggesting a chemotactic effect. Cell viability assays confirmed that none of the peptides exhibited cytotoxicity in PBMCs at tested concentrations, although BMAP27 reduced lymphocyte numbers (40% decrease, p < 0.0001), possibly indicating selective immunoregulatory effects. In BT cells, Bac5 enhanced proliferation (11% increase, p < 0.05), while BNBD1 (23% decrease, p < 0.01) and BMAP27 (10% decrease, p < 0.05) mildly reduced cellular impedance, reflecting divergent impacts on epithelial dynamics. CONCLUSIONS: These findings reveal distinct immunomodulatory profiles among bovine HDPs, ranging from pro-inflammatory (BNBD3, LAP) to suppressive (BMAP27), and underscore the importance of treatment timing. The immune-priming capacity of certain HDPs suggests potential use as prophylactic agents to enhance resilience to infections, while suppressive peptides like BMAP27 may serve therapeutic roles in resolving excessive inflammation. Importantly, the variability observed among individual animals emphasizes the need for personalized approaches in immunomodulation. Overall, this study provides novel insights into the immunological functions of bovine HDPs, supporting their potential as alternatives or adjunctive therapies to antibiotics in veterinary medicine.