Veterinary session

Enteric bacterial infections are a serious risk to the welfare of production animals. These infections can be difficult to treat because antibiotic resistance prevention calls for the prudent use of antibiotics. Pathogenic enteric bacteria release harmful toxins that can enter the portal system and reach the liver. Exposure to endotoxins leads to an immune response to fight infection and clear toxins from the body, and this can result in excess inflammation that is detrimental to animal welfare and production. For these reasons, the development of antimicrobial and anti-inflammatory therapies that can safely be used in production animals is of great importance. Antimicrobial peptides (AMP) show promise as novel therapies to combat infection and inflammation within the gut-liver axis. One group of AMPs of interest are cathelicidins. In this study, the immunomodulatory activities of chicken cathelicidin-2 were investigated in primary hepatocyte-non-parenchymal cell co-cultures exposed to the endotoxin lipoteichoic acid (LTA). After treatments with cathelicidin-2 alone or with cathelicidin-2 alongside LTA, metabolic activity and membrane damage were assessed with CCK and lactate dehydrogenase (LDH) assays, respectively. The concentration of cytokines interferon gamma (IFN-γ) and interleukin 10 (IL-10) were measured with Luminex assays and IL-8 levels were assessed using ELISA technique.

In this study, co-cultures showed a decrease in metabolic activity after treatment with cathelicidin-2, with a higher concentration of the AMP (10 nmol/mL) resulting in a greater decrease in activity than the lower concentration (5 nmol/mL). The LTA-exposed cultures treated with cathelicidin-2 also showed a dose-dependent decrease in metabolic activity. The LDH assay showed increased LDH levels for cells treated with cathelicidin-2 in the absence of LTA-induced inflammation. In the cells exposed to LTA, however, there were no significant differences in LDH levels compared to the negative control, even when the cells were treated with cathelicidin-2. With regards to cytokine measurements, cell cultures exposed to cathelicidin-2 showed a dose-dependent increase in production of IFN-γ, IL-8, and IL-10. Exposure to LTA yielded an increase in IFN-γ expression but the IL-8 and IL-10 concentrations in these samples showed no significant difference when compared to the negative control. When the LTA-exposed cells were treated with a lower concentration of cathelicidin-2 (5 nmol/mL), there was a decrease in IFN-γ levels compared to the LTA-only condition, therefore the lower level of cathelicidin successfully ameliorated the LTA-triggered IFN release. These results indicate that cathelicidin-2 plays an immunomodulatory role and influences both pro- and anti-inflammatory cytokine production in the liver, making it a promising candidate for treatment of harmful inflammatory diseases caused by bacterial infections.