Oral Galactooligosaccharide Administration Diminishes the Improvement in Allergy Severity Induced by Oral Immunotherapy in a Mouse Model of Egg White Allergy

Abstract

This study investigated how galactooligosaccharide (GOS) administration influences the efficacy of oral immunotherapy (OIT). Mouse models of egg allergy were prepared using alum as an adjuvant. The mice were divided into three groups: Non-OIT, OIT, GOS-administered, and OIT＋GOS-administered. Non-sensitized mice were also prepared. During a four-week treatment period, the OIT groups (OIT and OIT＋GOS) were fed a diet containing 1％ egg white, and the GOS groups (GOS and OIT＋GOS) were force-fed 30 mg of GOS daily. Allergy severity was evaluated following egg white oral and abdominal food challenge. Regulatory T cells (Tregs) were also examined as the ratio of CD4⁺ Foxp3⁺ cells among splenic lymphocytes. In the oral food challenge experiment after OIT, the decrease in the rectal temperature of the mice in the OIT group was suppressed relative to the decrease in the Non-OIT group; however, no such suppression was observed in the OIT＋GOS group. The CD4⁺ Foxp3⁺ (Treg) cell ratio was highest in the OIT group, followed in order by the OIT＋GOS group and the Non-OIT group. Therefore, the relationship between Tregs and OIT was also investigated. Interestingly, after 2 weeks of OIT in the model mice with reduced Tregs after administration of anti-mouse CD25 antibody, no suppression of the decrease in rectal temperature was observed following oral food challenge. We observed that combining GOS with OIT diminished the efficacy of OIT, potentially due to a reduction of Tregs.