Disclosed is a therapeutic agent for treating a cellular immune disease, comprising as an active ingredient a substance that inhibits binding between Sema3A and a Neuropilin-1/Plexin-A1 heteroreceptor. The substance includes, for example, a Sema3A neutralizing antibody, a Neuropilin-1 neutralizing antibody, or a soluble Neuropilin-1 or derivative thereof. Also disclosed is a method for screening a therapeutic agent for treating a cellular immune disease utilizing a signal generated by the interactions of Neuropilin-1, Plexin-A1 and Sema3A as a marker.
