Protective Association Between Allergen Immunotherapy and Adult-Onset Food AllergyTo the Editor:Subcutaneous (allergen) immunotherapy (SCIT) in patients with allergic rhinitis may prevent the progression of respiratory airway disease. Several small-scale studies have suggested that SCIT to pollen may help alleviate pollen-food allergy syndrome symptoms due to shared epitopes between tree pollen and edible plant allergens1, although it has not been recommended for primary desensitization2. In this study, we evaluated the relationship between SCIT and new onset food allergy in our outpatient study population.A retrospective cohort study of adults (n=94) receiving ongoing allergy care at our University Hospital in Brooklyn, NY, USA was conducted to investigate factors [including demographics, Body Mass Index (BMI), and SCIT] associated with new-onset, IgE-mediated food allergy (positive reaction history and skin-test or food-IgE) in adulthood. Informed consent requirements were waived upon institutional review (ethics) board approval. Statistical analyses included chi-square tests, Spearman’s correlation coefficients, and logistic regression.Demographic analysis included 23 men and 71 women with a mean age of 49.1 years, having a known diagnosis of respiratory allergy (allergic rhinitis and/or asthma) (n=85) and adult food allergy (n=33,Table 1 ). Clinical food allergy was diagnosed in 4/29 adults (13.8%) who had received SCIT and in 29/63 adults (46%) who had not received it (Figure 1 ). Food allergies were mostly to shrimp (n=19) followed by pineapple, kiwi, banana, avocado, nectarine, cashewnut, peanut, sesame, wheat, egg and tuna, and three to unknown food. BMI did not correlate significantly with SCIT, but correlated positively with adult food allergy, (r=0.469, p<0.001). Adult food allergy correlated negatively with receiving SCIT (r=-0.312, p=0.002).In logistic regression models, SCIT predicted significantly lower odds of adult-onset food allergy, after adjusting for age, sex, race, and BMI, (OR=0.132, 95% CI 0.028-0.618, p=0.010). BMI was independently associated with significantly higher odds of food allergy after adjusting for receiving SCIT, age, sex, and race (OR=1.189, 95% CI 1.085-1.303, p<0.001).Understanding allergenic cross-reactivity is crucial in the management of food allergy, which may be IgE-mediated (as seen between shrimp and dust mite tropomysins) or T cell-mediated. [as seen with Bet v 1 epitopes (e.g., birch pollen) cross-reacting with PR-10–like food allergens (e.g., apples)]3. Cross-reactive epitopes may help aid desensitization and clinical tolerance3. SCIT works in part by altering T and B cell-memory which may confer long-term clinical benefits. Murine studies show birch pollen SCIT reduces Th2 responses but not IL-33–mediated innate immunity linked to weight loss4. This aligns with clinical findings of lower BMI in SCIT-treated patients. House dust mite immunotherapy reduced specific-IgE to Der p 10 and Pen a 1 and eliminated seafood reactivity in one case5, and in a another study, prevented shrimp allergy in 70 patients over three years despite regular consumption6.In our study, SCIT protected against food allergy despite multiple covariate adjustment. We had previously reported that higher adult BMI was associated with adult-onset shrimp allergy and sensitization, independent of pre-existing cross-reactive sensitizations to dust mite and cockroach. This study also showed positive correlations between obesity and food allergy. Although the exact underlying mechanism is undetermined, our study suggests that obesity may epidemiologically modify the role of SCIT in adult-onset shrimp allergy. To our knowledge, this is the first study using both evaluate allergen immunotherapy in relation to adult-onset food allergy. Our study was limited by its small sample size from a single clinic in New York City which may limit external validity. Subcutaneous immunotherapy may be explored as a preventative therapeutic option for adult-onset food allergy, especially in patients with respiratory allergy and high BMI.