The present invention provides methods for diagnosing an immune-mediated disease, e.g., an autoimmune disease, an allergy or an inflammatory disease. Diagnosis is made by detecting a heterozygous or homozygous genotype of haptoglobin 2 or by detecting and quantifying pre-haptoglobin 2 mRNA or protein. After diagnosis, the disease may be treated by decreasing cell permeability leading to increased transepithelial electrical resistance, for example, by administering an antibody directed against single chain zonulin thereby inhibiting epidermal growth factor receptor and inhibiting proteinase-activated receptor 2 (PAR2).