An oral preparation for the prophylaxis or treatment of a disease with infection by a pathogen, containing a killed lactic acid bacterium expressing, on the surface, an antigen of the pathogen, or a microparticulated form thereof, which has an average particle size of 2.68 - 30 µm. An oral preparation for inducing cellular immunity to a target antigen, containing a killed lactic acid bacterium expressing the target antigen on the surface or a microparticulated form thereof, which has a particle size of 2.68 - 30 µm.
