Epithelial-Macrophage Crosstalk in Host Responses to Campylobacter jejuni Infection in Humans

Interactions between Campylobacter jejuni and host immune cells have been studied using various single-cell line models, such as macrophages and intestinal epithelial cells; however, these single-cell approaches do not fully capture the complexity of the host response. Investigating the interactions between these cell types offers a more comprehensive model for understanding Campylobacter-host dynamics. Therefore, this study aimed to investigate these interactions, specifically between intestinal epithelial cells and macrophages, using an in vitro model of C. jejuni infection. We examined whether soluble factors secreted from C. jejuni-infected HT-29 cells (human colorectal adenocarcinoma cells that express characteristics of mature intestinal cells) at 10 and 50 multiplicities of infection (MOI) influence RAW 264.7 macrophage activity, including nitric oxide (NO) production, migration, phagocytosis, bacterial killing, and the expression of cytokines (IL-6, IL-1β, TNF-α) and the chemokine CCL2. C. jejuni infection of HT-29 cells at 10 MOI induced significant IFN-γ production, a key macrophage activator. The treatment of macrophages with supernatants from HT-29 cells infected with C. jejuni significantly increased NO production, enhanced migration and phagocytic activity, and increased IL-6, TNF-α and CCL2 gene expression. However, no significant killing of phagocytosed C. jejuni was observed. On the other hand, supernatants from HT-29 cells infected with 50 MOI of C. jejuni suppressed NO production and macrophage phagocytosis, which may explain individual variations in the immune system's ability to contain infection, potentially influenced by the infectious dose. These findings support the notion that Campylobacter can evade macrophage killing even under activated conditions. Further studies are needed to elucidate the molecular mechanisms by which Campylobacter survives within activated macrophages.