Suppression of the immunologic response to peanut during immunotherapy is often transient

Background Studies suggest that oral immunotherapy (OIT) and sublingual immunotherapy (SLIT) for food allergy hold promise; however, the immunologic mechanisms underlying these therapies are not well understood. Objective We sought to generate insights into the mechanisms and duration of suppression of immune responses to peanut during immunotherapy. Methods Blood was obtained from subjects at baseline and at multiple time points during a placebo-controlled trial of peanut OIT and SLIT. Immunologic outcomes included measurement of spontaneous and stimulated basophil activity by using automated fluorometry (histamine) and flow cytometry (activation markers and IL-4), measurement of allergen-induced cytokine expression in dendritic cell (DC)-T-cell cocultures by using multiplexing technology, and measurement of MHC II and costimulatory molecule expression on DCs by using flow cytometry. Results Spontaneous and allergen-induced basophil reactivity (histamine release, CD63 expression, and IL-4 production) were suppressed during dose escalation and after 6 months of maintenance dosing. Peanut- and dust mite-induced expression of T_H2 cytokines was reduced in DC-T-cell cocultures during immunotherapy. This was associated with decreased levels of CD40, HLA-DR, and CD86 expression on DCs and increased expression of CD80. These effects were most striking in myeloid DC-T-cell cocultures from subjects receiving OIT. Many markers of immunologic suppression reversed after withdrawal from immunotherapy and in some cases during ongoing maintenance therapy. Conclusion OIT and SLIT for peanut allergy induce rapid suppression of basophil effector functions, DC activation, and T_H2 cytokine responses during the initial phases of immunotherapy in an antigen-nonspecific manner. Although there was some interindividual variation, in many patients suppression appeared to be temporary.