The purpose of the present invention is to elucidate a relationship between deregulation of signaling by CD22 and a rapid response of B cells by IgG-BCR and the like, and to provide a method capable of inducing a rapid immune response and defending against infection instead of vaccine. The present invention relates to a method for promoting an immune response causing such a strong proliferation of clones and production of a large amount of antibody-producing cells as those seen in the memory immune response even in the naive B cells expressing IgM-BCR and IgD-BCR by inhibiting the CD22 function in B cells； and to a method for screening a substance capable of promoting the immune response based on a change in the CD22 function in B cells.
