<;P>;PROBLEM TO BE SOLVED: To provide a regulatory T cell proliferation agent that improves regulatory T cells specifically in the intestinal tract in terms of numbers or functions; and to provide a food, a drink, a feed, or the like containing the regulatory T cell proliferation agent. <;P>;SOLUTION: The regulatory T cell proliferation agent comprises lactic acid bacteria belonging to Lactobacillus helveticus as an effective ingredient. <;P>;COPYRIGHT: (C)2011,JPO&INPIT