Human Invariant Natural Killer T Cells Respond to Antigen-Presenting Cells Exposed to Lipids from Olea europaea Pollen.

BACKGROUND: Allergic sensitization might be influenced by the lipids present in allergens, which can be recognized by natural killer T (NKT) cells on antigen-presenting cells (APCs). The aim of this study was to analyze the effect of olive pollen lipids in human APCs, including monocytes as well as monocyte-derived macrophages (Mϕ) and dendritic cells (DCs). METHODS: Lipids were extracted from olive (Olea europaea) pollen grains. Invariant (i)NKT cells, monocytes, Mϕ, and DCs were obtained from buffy coats of healthy blood donors, and their cell phenotype was determined by flow cytometry. iNKT cytotoxicity was measured using a lactate dehydrogenase assay. Gene expression of CD1A and CD1D was performed by RT-PCR, and the production of IL-6, IL-10, IL-12, and TNF-α cytokines by monocytes, Mϕ, and DCs was measured by ELISA. RESULTS: Our results showed that monocytes and monocyte-derived Mϕ treated with olive pollen lipids strongly activate iNKT cells. We observed several phenotypic modifications in the APCs upon exposure to pollen-derived lipids. Both Mϕ and monocytes treated with olive pollen lipids showed an increase in CD1D gene expression, whereas upregulation of cell surface CD1d protein occurred only in Mϕ. Furthermore, DCs differentiated in the presence of human serum enhance their surface CD1d expression when exposed to olive pollen lipids. Finally, olive pollen lipids were able to stimulate the production of IL-6 but downregulated the production of lipopolysaccharide- induced IL-10 by Mϕ. CONCLUSIONS: Olive pollen lipids alter the phenotype of monocytes, Mϕ, and DCs, resulting in the activation of NKT cells, which have the potential to influence allergic immune responses.

Olea europaea pollen lipids activate invariant natural killer T cells by upregulating CD1d expression on dendritic cells.

BACKGROUND: Invariant natural killer T (iNKT) cells recognize lipids presented by CD1d and have been implicated in the pathogenesis of allergic asthma. Recognition of plant pollen lipids by iNKT cells and their role in allergic responses are poorly defined. OBJECTIVE: Our goal was to investigate whether iNKT cells can be activated by monocyte-derived dendritic cells (DCs) exposed to lipid antigens from Olea europaea. METHODS: DCs generated in vitro were exposed to O europaea pollen grains or lipids isolated from them. Expression of lipid-presenting molecules (CD1), as well as maturation markers (HLA-DR, HLA-I, CD86, and CD80 molecules), on DCs was analyzed. iNKT cell activation after coculture with DCs was evaluated based on expansion, cytokine production, and cytotoxicity tests. RESULTS: DCs upregulated CD1d and CD86 expression and downregulated CD1a expression after exposure to a whole extract of olive pollen lipids. CD1d and CD1a were regulated at the transcriptional level in a peroxisome proliferator-activated receptor γ activation-dependent manner. Polar lipids, diacylglycerols, free fatty acids, and triacylglycerols isolated from pollen grains upregulate CD1d. The increase in CD1d expression on the DC cell surface induced by polar lipids was not regulated at the RNA level. iNKT cells efficiently recognize DCs treated with the different lipids isolated from olive pollen grains. CONCLUSIONS: Lipids from O europaea pollen upregulate CD1d and CD86 molecules on DCs, which are then able to activate iNKT cells through a CD1d-dependent pathway.