Comparison of adjuvant mechanisms of medium-chain triacylglycerol in a mouse FITC-induced contact hypersensitivity model

The number of allergy sufferers has been increasing with the increase in chemicals to which we are potentially exposed. We have discovered that tributyrin, a short-chain triacylglycerol (TAG), enhanced fluorescein isothiocyanate (FITC)-induced contact hypersensitivity in a mouse model. Medium-chain triacylglycerols (MCTs) are used in cosmetics, with which we come into direct contact frequently, to maintain skin conditions and as a thickening agent for cosmetics. In this study, we examined whether MCTs with different side chain lengths enhanced skin sensitization to FITC in the mouse model. During skin sensitization to FITC, the presence of tributyrin (side chain carbon number, 4; C4) as well as that of each MCT, tricaproin (C6), tricaprylin (C8), or tricaprin (C10), resulted in enhanced skin sensitization, whereas that of trilaurin (C12) did not. As to the mechanism underlying the enhanced sensitization, three MCTs (C6, C8 and C10) facilitated migration of FTIC-presenting CD11c⁺ dendritic cells to draining lymph nodes. These results indicated that not only tributyrin but also MCTs, up to side chain carbon number 10, have an adjuvant effect on FITC-induced skin hypersensitivity in mice.

Enhancement of mouse contact hypersensitivity appears with a short chain triacylglycerol but not with a long chain one

The prevalence of skin allergies could be partly due to the increased exposure to chemicals from consumer products. Chemicals that can enhance hypersensitivity caused by other chemicals are the focus of this study. We have demonstrated that phthalate esters with short chain alcohols enhance fluorescein isothiocyanate (FITC)-induced contact hypersensitivity (CHS) in a mouse model. We have also found that tributyrin, a triacylglycerol (TAG) with three butyric acids, enhances sensitization to FITC. To elucidate such an enhanced skin sensitization might be based on a general feature of TAG, we compared tributyrin and triolein, a natural TAG, as to an adjuvant effect on FITC-CHS. Triolein is the dominant TAG in olive oil and contains long chain mono-unsaturated fatty acids. Unlike tributyrin and dibutyl phthalate (DBP), triolein did not exhibit an adjuvant effect. With triolein, enhancement of FITC-presenting CD11c⁺ dendritic cell trafficking to draining lymph nodes was weak, and the activation status of DC, as revealed as CD86 expression, was low. We found a difference in the pattern of skin cytokine production, i.e., that thymic stromal lymphopoietin was produced with DBP and interleukin-1β with tributyrin. Triolein did not induce either of these cytokines. This illustrates that the adjuvant effect of tributyrin on FITC-CHS is not a general phenomenon for TAGs. Although beneficial effects may be expected through oral administration of tributyrin, the effect on skin immune systems should be considered.

Skin Sensitization to Fluorescein Isothiocyanate Is Enhanced by Butyl Paraben in a Mouse Model

Contact hypersensitivity (CHS) to preservatives is receiving increased attention. Parabens are widely used in foods, pharmaceutics and cosmetics as preservatives. The skin sensitizing activity of parabens remains controversial but a few investigations have been made as to whether parabens could facilitate sensitization to other chemicals. We have shown that di-n-butyl phthalate (DBP), a phthalate ester, has an adjuvant effect in a fluorescein isothiocyanate (FITC)-induced CHS mouse model. We have also demonstrated that DBP activates transient receptor potential ankyrin 1 (TRPA1) cation channels expressed on sensory neurons. Comparative studies of phthalate esters revealed that TRPA1 agonistic activity and the adjuvant effect on FITC-CHS coincide. Here we focused on two commonly used parabens, butyl paraben (BP) and ethyl paraben (EP), as to their adjuvant effects. BALB/c mice were epicutneously sensitized with FITC in acetone in the presence or absence of a paraben. Sensitization to FITC was evaluated as the ear-swelling response after FITC challenge. BP but not EP enhanced skin sensitization to FITC, but the effect of BP was much weaker than that of DBP. Mechanistically, BP enhanced the trafficking of FITC-presenting CD11c⁺ dendritic cells (DCs) from the skin to draining lymph nodes as well as cytokine production by draining lymph nodes. When the TRPA1 agonistic activity was measured with a cell line expressing TRPA1, BP exhibited higher activity than EP. The present study provides direct in vivo evidence that BP causes sensitization to other chemicals by means of a mouse FITC-CHS model.

The Role of Interleukin-19 in Contact Hypersensitivity

Interleukin (IL)-19 is a member of the IL-10 family of interleukins and is an immuno-modulatory cytokine produced by the main macrophages. The gastrointestinal tissues of IL-19 knockout mice show exacerbated experimental colitis mediated by the innate immune system and T cells. There is an increasing focus on the interaction and relationship of IL-19 with the function of T cells. Contact hypersensitivity (CHS) is T cell-mediated cutaneous inflammation. Therefore, we asked whether IL-19 causes CHS. We investigated the immunological role of IL-19 in CHS induced by 1-fluoro-2,4-dinitrofluorobenzene as a hapten. IL-19 was highly expressed in skin exposed to the hapten, and ear swelling was increased in IL-19 knockout mice. The exacerbation of the CHS response in IL-19 knockout mice correlated with increased levels of IL-17 and IL-6, but no alterations were noted in the production of interferon (IFN)γ and IL-4 in the T cells of the lymph nodes. In addition to the effect on T cell response, IL-19 knockout mice increased production of inflammatory cytokines. These results show that IL-19 suppressed hapten-dependent skin inflammation in the elicitation phase of CHS.