Chitin and its derivative chitosan differently activate porcine innate immune cells

In livestock species such as pigs, antibiotics are frequently used during weaning, a period of increased susceptibility to infections. However, the emergence and spread of antimicrobial resistance necessitate alternative strategies to improve animal health. Immune potentiating polysaccharides, including chitin, chitosan, and their derivatives, show promise as functional feed ingredients, yet their direct effects on porcine innate immune cells remain unclear. Here, ex vivo porcine primary neutrophils, monocytes, and monocyte-derived macrophages were used to assess the immunomodulatory properties of structurally distinct chitin-based polymers. In peripheral blood mononuclear cells, neither chitin nor chitosan induced significant secretion of IL-1β, TNF-α, or IL-6, suggesting that only specific subpopulations mediate these effects. Following fractionation, cytokine production was restricted to the CD14⁺ monocyte compartment, where high concentrations of chitosan elicited strong pro-inflammatory responses. To further investigate innate immune programming, trained immunity assays were performed. In monocytes, chitin did not induce training or tolerance, whereas low-molecular-weight, highly deacetylated chitosan promoted a trained phenotype, evidenced by enhanced cytokine production upon lipopolysaccharide restimulation. In contrast, in monocyte-derived macrophages, chitin pretreatment induced a tolerance-like phenotype, characterized by reduced cytokine responses following subsequent stimulation, while chitosan had no significant effect. These findings demonstrate that structural differences in chitin-based polymers determine the magnitude and direction of innate immune responses, supporting their targeted use as functional immunomodulators to enhance health and resilience in livestock.