Evaluation of immunomodulatory effects of Boswellia sacra essential oil on T-cells and dendritic cells

Abstract

Background: Boswellia sacra resin has been commonly used as analgesic, antimicrobial, and anti-inflammatory properties, which reflect its immunomodulatory activity. Dendritic cells (DCs) are specialized antigen-presenting cells (APCs) and sentinel cells that regulate the immune response. This study aims at investigating whether crude essential oil extracted from Boswellia sacra resin (BSEO), has a potential effect on the phenotype and functions of human monocyte-derived DCs.

Methods: Oil extract from the resin of Boswellia sacra was prepared by hydrodistillation using a custom made hydrodistiller. BSEO-mediated cell viability has been initially studied on human skin dermis cells (HSD) and DC precursors using quantitative and qualitative assays before applying on DCs. Human DCs were generated from differentiated peripheral blood monocytes cultured in media containing both GM-CSF and IL-4. DCs were exposed to 5 μg/mL or 10 μg/mL of BSEO in vitro. Morphological, phonotypical, and functional properties studied with microscopy, flow cytometry, and ELISA.

Results: Crude BSEO was found to interfere with the maturation and differentiation of DCs from precursor cells in the presence or absence of lipopolysaccharide (LPS). BSEO-treated DCs, cultured in the presence of LPS, reduced the ability of allogeneic T cells to proliferate compared to that co-cultured with LPS-stimulated DCs only. In addition, the endocytic capacity and secretion of IL-10 by DCs treated with BSEO was enhanced in comparison to LPS treated cells. Analysis of the chemical composition of BESO using GC-MS (Clarus 500 GC/MS, PerkinElmer, Shelton, CT) revealed the presence of compounds with several biological activities including antibacterial, antioxidant, and anti-inflammatory properties.

Conclusion: Results indicated that BSEO deviates the differentiation of monocytes into immature DCs. Furthermore, stimulation of immature DCs with BSEO was unable to generate full DC maturation. However, these findings may potentially be employed to generate DCs with tolerogenic properties that are able to induce tolerance in diseases with hypersensitivity, autoimmunity as well as transplantation.

Keywords: And tolerance; Boswellia sacra; Dendritic cells; Differentiation; Essential oil; Maturation.

Fig. 1

Morphology of DCs treated with crude BSEO. DCs were treated with either crude BSEO or LPS for 24 h and visualized using an inverted microscope. a Represents 0.1%DMSO-treated DCs that show a typical morphology of imDCs, which appeared irregular shape with short cytoplasmic projections. b Represents LPS-treated DCs that show a typical morphology of mDCs which seen elongated with long cytoplasmic projection. c Represents DCs treated with 5 μg/mL of BSEO and d DCs treated with 10 μg/mL of BSEO that exhibited imDCs features. Arrows pointed to DC projections. Photographed by phase-contrast inverted microscope (Original magnifications were 400X) at Immunology unit, KFMRC, King Abdulaziz University

Fig. 2

Effects of crude BSEO on T cell proliferation. Data represented the mean percentages of CD3⁺CD71⁺ T cells (± SD) co-cultured with stimulated DCs as determined using MLR assay. Results were performed from five independent experiments. Mean was significant when compared to LPS-stimulated DCs (*P < 0.05, **P < 0.01)

Fig. 3

Total ion GC-MS chromatogram of characterized volatile compounds of Boswellia sacra resin oil extracted by hydro-distillation