Immune priming reprograms the maggot secretome to enhance anti-Leishmania activity

Abstract Cutaneous leishmaniasis remains a major unmet medical need due to treatment toxicity, emerging drug resistance, prolonged therapy, and persistent tissue damage. Lucilia sericata (Diptera: Calliphoridae) larvae are a promising source of bioactive secretions with antimicrobial and wound-healing properties. Here, we investigated whether immune priming of L. sericata larvae with Leishmania major modulates the anti-leishmanial activity and metabolic profile of larval-derived products. Larvae underwent oral, intrahemocoelic, or combined priming, and their excretory/secretory (E/S) products and total-body extracts were evaluated against L. major promastigotes. Combined priming produced the strongest anti-leishmanial activity at 24 h, reducing parasite viability to 35.26% in E/S products. IC₅₀ values were 176.9 µg/mL for total-body extracts and 248.5 µg/mL for E/S products. LC-MS profiling revealed extensive metabolic remodeling, characterized by enrichment of molecular features putatively associated with antimicrobial peptides, flavonoids, and lipid metabolites, alongside depletion of several primary metabolic intermediates. These findings are consistent with a shift toward defense-associated metabolism and enhanced antiparasitic activity following immune priming. Overall, immune priming reprogrammed the larval secretome and enhanced its in vitro activity against L. major , supporting further investigation of cell-free larval-derived products as candidate bioactive preparations for cutaneous leishmaniasis.