IGFBP4 and allergic asthma: Serum PAPP-A, an insulin-like growth factor binding protein 4 protease (IGFBP-4), has been previously reported to be higher in the serum of patients with asthma compared to patients without asthma28,29 and in patients with severe allergic asthma treated with the anti-IgE monoclonal antibody omalizumab, PAPP-A serum levels were reduced.29