Salmonella enterica serovar Typhimurium travels to mesenteric lymph nodes both with host cells, and autonomously

Salmonella infection is a globally important cause of gastroenteritis and systemic disease, and is a useful tool to study immune responses in the intestine. Although mechanisms leading to immune responses against Salmonella have been extensively studied, questions remain about how bacteria travel from the intestinal mucosa to the mesenteric lymph nodes (MLN), a key site for antigen presentation. Here, we used a mouse model of infection with Salmonella enterica serovar Typhimurium (STM) to identify changes in intestinal immune cells induced during early infection. We then used fluorescently-labelled STM to identify interactions with immune cells, from the site of infection, through migration in lymph, to the MLN. We show that viable STM can be carried in the lymph by any subset of migrating dendritic cells, but not by macrophages. Moreover, approximately half of the STM in lymph are not associated with cells at all, and travel autonomously. Within the MLN, STM associates with dendritic cells and B cells, but predominantly with MLN-resident macrophages. In conclusion, we describe the routes used by STM to spread systemically in the period immediately after infection. This deeper understanding of the infection process could open new avenues for controlling it