<;P>;PROBLEM TO BE SOLVED: To provide a microorganism enhancing the effect of vaccine through humoral immunity and simultaneously preventing virus infection through cell-mediated immunity; and to provide uses thereof. <;P>;SOLUTION: There are disclosed Lactobacillus pentosus YM2-2 strain, and a mucosal immunostimulator, an IgA production promoting agent, a virus (especially rotavirus) infection protective agent, and foods and drinks, wherein these comprise the strain as an active ingredient. <;P>;COPYRIGHT: (C)2011,JPO&INPIT