PROBLEM TO BE SOLVED: To provide a lactic acid bacterium having a favorable particle diameter for Th1 induction, excellent in the productivity of INF-α, and excellent in dispersibility in water.SOLUTION: A bacterial cell of a nano-type lactic acid bacterium is obtained by adjusting a pH in a medium in a culturing step and a processing step of the lactic acid bacterium to a neutral range, wherein a mode value in a particle size distribution is 1.0 μm or less and the lactic acid bacterium is lactobacillus brevis.
