Background Allergy and autoimmunity are two potential outcomes of a dysregulated immune system, but the relationship between them is unclear. It has been hypothesized that they could be inversely associated because of different T helper cell reactivity patterns. However, both positive and negative associations have been reported. Therefore, our aim was to perform a large epidemiological study with a defined allergic disease cohort.
Methods During the years 1990–2002, 68 770 subjects were tested for total serum IgE (Total-IgE) and 72 228 were tested with Phadiatop for diagnosing allergic disease at Karolinska University Hospital, Stockholm, Sweden. This cohort was then linked with the Swedish Inpatient Registry 1968–2004 for a follow-up with regard to recorded discharges for 28 autoimmune diseases. We then used Cox regression and logistic regression to estimate the risk of autoimmune diseases in general in the allergy-tested subjects.
Results Subjects with positive Phadiatop test were at a statistically decreased risk of subsequent autoimmune disease in comparison with subjects with negative test; hazard ratio (HR): 0.80 [95% (Confidence interval) CI: 0.68–0.94). Prior autoimmune disease was associated with a decreased risk of positive Phadiatop test [odds ratio: 0.83 (95% CI: 0.72–0.96)] in comparison with negative test. Subjects with highly elevated Total-IgE were at a statistically increased risk of a subsequent autoimmune disease in comparison with subjects with normal levels [HR: 1.36 (95% CI: 1.09–1.70)], but no association was found between prior autoimmune disease and different Total-IgE levels.
Conclusion The study supports the hypothesis that allergy, defined as positive Phadiatop test, could be inversely related to autoimmune disease but this association is weak.