A type IV collagen-like immunoreactive peptide and an antibody thereof which are useful for detecting nephritis, a method for selecting a type IV collagen-like immunoreactive peptide, a method for screening an immunoreactive antibody and an immunoreactive peptide, a nephritis model, a method for detecting chronic nephritis, a vaccine, and a therapeutic agent for nephritis are provided.A type IV collagen-like immunoreactive peptide immunologically reacts with an isolated, chronic nephritis-derived biological sample. Preferably, the type IV collagen-like immunoreactive peptide includes at least one member selected from the group consisting of at least one chain selected from alpha 1 to alpha 6 chains as a constituent alpha chain, at least one region selected from 7S, the central helical domain, and NC1 as a constituent region, and a peptide having 3 to 35 amino acids as a constituent peptide.