The present disclosure relates to a composition for promoting immune activity including a protein selected from the group consisting of dimeric proinsulin, C-peptide partially deleted mutant of dimeric proinsulin, and C-peptide partially deleted mutant of monomeric proinsulin as an effective component and a composition for immunosuppression including C-peptide site of proinsulin as an effective component, and the dimeric proinsulin, the C-peptide partially deleted mutant of dimeric proinsulin, and the C-peptide partially deleted mutant of monomeric proinsulin can be applied as immune enhancers to diabetic patients.