Human antigen-presenting cells respond differently to gut-derived probiotic bacteria but mediate similar strain-dependent NK and T cell activation

The intestinal microbiota is essential for development and homeostasis of the local and systemic immune system, and particularly strains of lactic acid bacteria and Escherichia coli have been shown to have balancing effects on inflammatory conditions such as allergy and inflammatory bowel disease. However, distinct strains possess different potential to polarise and regulate the immune response, and in vitro results used to choose strains for therapeutic purposes may depend strongly on the cell type used as a model. We compared the response of three types of human antigen-presenting cells (blood myeloid dendritic cells, monocyte-derived dendritic cells and monocytes) to strains of intestinal bacteria, and characterised the effector response of natural killer cells and naïve T cells. The response to gut-derived bacteria was markedly different between antigen-presenting cells as concerns maturation and induction of pro-inflammatory cytokines, with blood dendritic cells and monocytes responding with production of interleukin-6 and tumour necrosis factor- to strains, which elicited anti-inflammatory responses in monocyte-derived dendritic cells. In contrast, an interferon- inducing capability of antigen-presenting cells cultured with specific bacterial strains and an interferon--inhibitory capability of other strains were generally observable with all types of antigen-presenting cells, and in both natural killer cells and T cells.