Dietary medium-chain triglycerides promote oral allergic sensitization and orally induced anaphylaxis to peanut protein in mice

Abstract

Background: The prevalence of peanut allergies is increasing. Peanuts and many other allergen sources contain significant amounts of triglycerides, which affect absorption of antigens but have unknown effects on sensitization and anaphylaxis. We recently reported that dietary medium-chain triglycerides (MCTs), which bypass mesenteric lymph and directly enter portal blood, reduce intestinal antigen absorption into blood compared with long-chain triglycerides (LCTs), which stimulate mesenteric lymph flow and are absorbed in chylomicrons through mesenteric lymph.

Objective: We sought to test how dietary MCTs affect food allergy.

Methods: C3H/HeJ mice were fed peanut butter protein in MCT, LCT (peanut oil), or LCT plus an inhibitor of chylomicron formation (Pluronic L81). Peanut-specific antibodies in plasma, responses of the mice to antigen challenges, and intestinal epithelial cytokine expression were subsequently measured.

Results: MCT suppressed antigen absorption into blood but stimulated absorption into Peyer patches. A single gavage of peanut protein with MCT, as well as prolonged feeding in MCT-based diets, caused spontaneous allergic sensitization. MCT-sensitized mice experienced IgG-dependent anaphylaxis on systemic challenge and IgE-dependent anaphylaxis on oral challenge. MCT feeding stimulated jejunal-epithelial thymic stromal lymphopoietin, Il25, and Il33 expression compared with that seen after LCT feeding and promoted T(H)2 cytokine responses in splenocytes. Moreover, oral challenges of sensitized mice with antigen in MCT significantly aggravated anaphylaxis compared with challenges with the LCT. Importantly, the effects of MCTs could be mimicked by adding Pluronic L81 to LCTs, and in vitro assays indicated that chylomicrons prevent basophil activation.

Conclusion: Dietary MCTs promote allergic sensitization and anaphylaxis by affecting antigen absorption and availability and by stimulating T(H)2 responses.

Figure 1

Effect triglycerides on antigen absorption. (A) Plasma ¹²⁵I 30 mins after gavage of radiolabeled peanut protein with indicated vehicles (n=6). (B) PL81 blocks LCT absorption as reflected by increased buoyancy due to lipid entrapment. Tissue was obtained 5h after gavage. (C and D) CD11c+ and DQ-OVA+ cells in Peyer's patches 16h after DQ-OVA gavage in indicated vehicles (n=4).

Figure 2

MCT causes allergic sensitization. Anti-peanut antibodies (A,-C) 18 days after gavage with peanut protein (80 mg) in indicated vehicles (n=6). LCT in A,B was peanut oil, in C soybean oil. (D) Splenocyte IL-13 release (n=4). (E) Gavage of peanut protein in LCT (OT) one week before gavage with MCT induces oral tolerance (n=6). (F) Anti-OVA IgE 18 days after gavage with OVA (60 mg) in indicated vehicles (n=6).

Figure 3

TSLP mRNA in epithelial cells of the jejunum 5h after gavage of 0.2 ml MCT, LCT, or saline (A) or 0.2 ml LCT, LCT + PL81, or saline + PL81 (B). N=6.

Figure 4

Effect MCT feeding on intestinal epithelial Th2 cytokine expression. (A) TSLP mRNA in epithelia from indicated sections 3 weeks after feeding (n=5). (B) IL-25 and IL-33 mRNA in jejunal epithelial cells 3 weeks after feeding (n=5). (C) IgE against peanut protein during 4 weeks feeding with diets enriched with peanut flour (n=6).

Figure 5

Promotion of Th2 responses by dietary MCT. DO11.10 mice were fed MCT or LCT- based diets containing egg white (“MCT+egg”, “LCT+egg”) or without egg white (“MCT”, “LCT”) egg white (n=5 per group). One week later, splenocytes were stimulated ex vivo with OVA peptide and indicated cytokines were measured with ELISA.

Figure 6

IgG-dependent anaphylaxis upon systemic challenge. Mice were gavaged once with peanut butter protein in indicated vehicles, then challenged by i.p. injection 18 days later (n=6). Parameters included plasma mmcp-1 90 minutes after the challenge (A), body temperature (B), and clinical score (C). Pretreatment with blocking antibodies against IgG receptors (2.4G2), but not against IgE (EM-95), blunted anaphylaxis (D).

Figure 7

IgE-dependent orally induced anaphylaxis is aggravated by MCT. (A) Body temperature of mice (n=6-7) challenged with peanut protein in MCT with or without pre-treatment with IgE blocking antibody. Sensitization occurred by gavage on days 1 and 8, challenges were performed on day 48. In (B), Mice (n=6) were sensitized as in (A), but the oral challenge was performed by gavage of peanut protein in different vehicles. (C) shows plasma mmcp-1 levels in mice in panel (B). (D) shows inhibition of basophil activation by including Intralipid (two different dilutions) with OVA added to sensitized basophils (n=4 per group). In (E), BALB/c mice (n=9 per group) were sensitized I.P. with OVA in alum, then challenged with 60 mg OVA by gavage in the indicated vehicle. All experiments were repeated at least twice with similar outcome, except B and C, which were performed once.