A placebo-controlled trial of immunotherapy with two extracts of Dermatophagoides pteronyssinus in allergic rhinitis, comparing clinical outcome with changes in antigen-specific IgE, IgG, and IgG subclasses.

A double-blind, placebo-controlled trial of immunotherapy was conducted in patients with Dermatophagoides pteronyssinus rhinitis. Thirty patients received an extract with a high content of Der p I (Pharmalgen), 20 received a conventional mite extract (Allpyral), and 30 patients received histamine chloride (placebo). Specific IgG and subclasses were measured before and after 3 and 12 months of treatment by RIA and/or ELISA, and specific IgE by RAST. Clinical outcome was assessed by skin prick tests, nasal challenge, visual analogue, and diary-card symptom and drug scores; from these findings, a clinical index was derived. An IgG response occurred only in the Pharmalgen-treated group: D. pter IgG and IgG1 increased by 3 months (p less than 0.05) and then plateaued to 12 months (p less than 0.05). IgG4 levels increased throughout treatment (p less than 0.05 and p less than 0.01), as did the IgG/IgE ratio. A subclass switch from IgG1 to IgG4 occurred. D. pter IgE rose at 3 months (p less than 0.05). Clinical improvement occurred at 3 and 12 months in the Pharmalgen-treated group only. Pretreatment levels of IgE, IgG1, or IgG4 did not predict clinical outcome. Our findings are compatible with the hypothesis that IgG subclasses may modulate antigen-IgE interactions, although the antibody response to this potent extract need not be causally related to improvement.