Intestinal commensal bacteria is now recognized to be an important element in the control of the development and function of the host immune system, including the production of secretory IgA and differentiation of specific T cell populations. Although many studies mainly focused on the commensal bacteria in the intestinal lumen or mucus layers, genome-based bacterial analysis using intestinal tissue allowed us to identify Alcaligenes as symbiotic resident bacteria of Peyer's patches (PPs), a major gut-associated lymphoid tissue in the small intestine, which is regulated by type 3 innate lymphoid cells (ILC3) . Our subsequent study showed that Alcaligenes have a greater ability to survive in dendritic cells (DCs) and modulate the production of cytokines such as IL-1b, IL-6, IL-10, IL-12p40, and IL23 from DCs. We recently found that lipopolysaccharide (LPS) of Alcaligenes acts as a weak TLR4 agonist and thus creates a homeostatic inflammatory condition that includes IgA responses in PPs without the excessive pathological inflammation These findings allowed us to apply Alcaligenes LPS could be used as a safe and effective vaccine adjuvant.