A case of allergy to human insulin associated with high IgG/IgE ratio for specific antibodies

A 37-year-old woman with a previous history of allergic rhinitis and bronchial asthma presented local and generalized allergic reactions to bovine, porcine and human insulins. She developed ketoacidosis, high insulin requirements and transient hypoglycemic episodes. Several desensitizing schedules were applied in order to induce tolerance to human insulin therapy. In addition, the following parameters of the humoral immune response were measured in different serum samples taken within 13 days after one of the anaphylactic episodes: insulin antibodies (binding range = 29.4-47.8%; cutoff = 2.6%), total IgE (range = 500-850 IU/ml; normal values = 3.7-269 IU/ml), specific IgE (range = 0.42-0.83 PRU/ml; class 2) and subclasses of specific IgG (IgG1 = 97.2 SDS; IgG2 = 41.1 SDS; IgG3 = 9.9 SDS; IgG4 = 0.3 SDS, on day 1). A binding capacity of 31.8 IU insulin/l obtained by Scatchard analysis was in agreement with episodes of elevated insulin requirements and hypoglycemia. A high anti-insulin IgG/IgE ratio, along with high levels of specific IgG1 antibodies, suggested that the latter antibodies could be involved in the development of anaphylactic episodes.