Lipid Mediators From Timothy Grass Pollen Contribute to the Effector Phase of Allergy and Prime Dendritic Cells for Glycolipid Presentation.

Plant pollen are an important source of antigens that evoke allergic responses. Protein antigens have been the focus of studies aiming to elucidate the mechanisms responsible for allergic reactions to pollen. However, proteins are not the sole active agent present in pollen. It is known that pollen grains contain lipids essential for its reproduction and bioactive lipid mediators. These small molecular compounds are co-delivered with the allergens and hence have the potential to modulate the immune response of subjects by activating their innate immune cells. Previous reports showed that pollen associated lipid mediators exhibited neutrophil- and eosinophil-chemotactic activity and induced polarization of dendritic cells (DCs) toward a Th2-inducing phenotype. In our study we performed chemical analyses of the pollen associated lipids, that are rapidly released upon hydration. As main components we have identified different types of phytoprostanes (PhytoPs), and for the first time phytofurans (PhytoFs), with predominating 16-F1t-PhytoPs (PPF1-I), 9-F1t-PhytoPs (PPF1-II), 16-E1t-PhytoPs (PPE1-I) and 9-D1t-PhytoPs (PPE1-II), and 16(RS)-9-epi-ST-Δ14-10-PhytoFs. Interestingly 16-E1t-PhytoP and 9-D1t-PhytoPs were found to be bound to glycerol. Lipid-containing samples (aqueous pollen extract, APE) induced murine mast cell chemotaxis and IL-6 release, and enhanced their IgE-dependent degranulation, demonstrating a role for these lipids in the immediate effector phase of allergic inflammation. Noteworthy, mast cell degranulation seems to be dependent on glycerol-bound, but not free phytoprostanes. On murine dendritic cells, APE selectively induced the upregulation of CD1d, likely preparing lipid-antigen presentation to iNKT cells. Our report contributes to the understanding of the activity of lipid mediators in the immediate effector phase of allergic reactions but identifies a yet undescribed pathway for the recognition of pollen-derived glycolipids by iNKT cells.

NKT cells can help mediate the protective effects of 1,25-dihydroxyvitamin D3 in experimental autoimmune encephalomyelitis in mice.

Active vitamin D [1,25-dihydroxyvitamin D3 (1,25D3)] blocks the development of experimental autoimmune diseases. However, the molecular and immunobiological mechanisms underlying 1,25D3's anti-inflammatory properties are not fully understood. We employed a murine model of experimental autoimmune encephalomyelitis (EAE) in order to determine the role of NKT cells in 1,25D3-mediated protection from EAE. Wild-type (WT) mice or mice lacking all NKT cells (CD1d(-/-)) or invariant NKT cells (Jα18(-/-)) were fed control or 1,25D3-supplemented diets. All mice fed with the control diet developed severe EAE. 1,25D3 treatment of WT mice protected them from developing EAE. CD1d(-/-) and Jα18(-/-) mice treated with 1,25D3 were not protected to the same extent as WT mice. Myelin oligodendrocyte glycoprotein-specific IL-17 and IFN-γ production was significantly reduced in 1,25D3 WT mice compared with WT but was not decreased in 1,25D3 CD1d(-/-) mice compared with CD1d(-/-) mice. IL-4(-/-) mice were utilized to determine how IL-4 deficiency affects susceptibility to EAE. IL-4(-/-) mice were not protected from developing EAE by α-galactosylceramide (α-GalCer) or 1,25D3 treatment. Furthermore, 1,25D3 treatment of splenocytes in vitro decreased α-GalCer-induced IL-17 and increased IL-4, IL-5 and IL-10 production. 1,25D3 alters the cytokine profile of invariant NKT cells in vitro. These studies demonstrate that NKT cells are important mediators of 1,25D3-induced protection from EAE in mice and NKT cell-derived IL-4 may be an important factor in providing this protection.

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.

Significance of para-esophageal lymph nodes in food or aeroallergen-induced iNKT cell-mediated experimental eosinophilic esophagitis.

Eosinophilic esophagitis (EoE) is a recently recognized inflammatory disorder driven by food hypersensitivity; however, the specific foods and mechanisms involved are unclear. In patients with EoE, we have found that hypersensitivities to corn and peanuts are the most common. Accordingly, we sensitized and exposed mice either intranasally or intragastrically with corn or peanut extract or saline. Esophageal eosinophilia, the genes of eosinophil-directed cytokines, and allergen-induced antibodies were examined in mice challenged with corn or peanut extract or saline. A high number of esophageal lamina propria eosinophils as well as eosinophilic microabscesses, intraepithelial eosinophils, extracellular eosinophilic granules, thickened and disrupted epithelial mucosa, and mast cell hyperplasia were observed in the esophagus of peanut or corn allergen-challenged mice. Mechanistic analysis indicated that para-esophageal lymph nodes might be critical in the trafficking of eosinophils to the esophagus and in EoE association to airway eosinophilia. Furthermore, experimentation with gene-targeted mice revealed that peanut allergen-induced EoE was dependent on eotaxin and invariant natural killer T (iNKT) cells, as CD1d and eotaxin-1/2 gene-deficient mice were protected from disease induction. Thus we provide evidence that para-esophageal lymph nodes are involved in food- or aeroallergen-induced eosinophilia and patchy EoE pathogenesis, likely a mechanism dependent on eotaxins and iNKT cells.

Retinoic acid and α-galactosylceramide differentially regulate B cell activation in vitro and augment antibody production in vivo.

All-trans-retinoic acid (RA) promotes the maturation and differentiation of B cells, which are known as a type of professional antigen-presenting cells. We show here that CD1d, a major histocompatibility complex class I-like molecule that presents lipid antigens, is expressed in the mouse spleen B cells and is increased by RA. Thus, we hypothesized that RA and the CD1d ligand, α-galactosylceramide (αGalCer), could interact to promote the differentiation, maturation, and antibody response of antigen-activated B cells. In isolated B cells, αGalCer alone markedly stimulated, and RA further increased B cell proliferation, synergizing with the B cell antigen receptor ligation via anti-µ antibody (P < 0.05). The significantly increased cell proliferation stimulated by αGalCer was abrogated in the B cells of CD1d-null mice. RA alone and combined with αGalCer also promoted B cell differentiation by the enrichment of sIgG1-, CD138-, and PNA/Fas-positive B cells (P < 0.05), suggesting a plasmacytic cell differentiation. In vivo, wild-type mice treated with RA and/or αGalCer during primary immunization with tetanus toxoid produced a higher serum anti-tetanus IgG response and had more bone marrow anti-tetanus antibody-secreting cells as determined by enzyme-linked immunospot assay (P < 0.05) in the secondary response, a finding indicative of heightened long-term memory; however, the increased antibody secretion after αGalCer treatment was abolished in CD1d-null mice. We provide evidence here that RA, together with αGalCer, can effectively regulate B cell proliferation and differentiation, ultimately promoting a more efficient antibody response to protein antigen. The results suggest that the combination of RA and αGalCer could be a useful adjuvant combination in vaccine strategies.

Regulation of multiple myeloma survival and progression by CD1d.

Down-regulation of conventional human leukocyte antigen (HLA) class I and II molecules from the surface of tumor cells is an important mechanism for tumor immune evasion, survival, and progression. Whether CD1d, a nonconventional, glycolipid-presenting HLA class I-like molecule instructing the function of the immunoregulatory invariant NKT cells can affect tumor cell survival is not known. Here we show that CD1d is highly expressed in premalignant and early myeloma, but with disease progression its expression is reduced and eventually in advanced stages and myeloma cell lines is lost altogether, suggesting that CD1d impacts negatively on myeloma cell survival. Consistent with this, engagement of CD1d by anti-CD1d monoclonal antibodies (mAbs) induces cell death of myeloma cell lines with restored CD1d expression and primary myeloma cells. Cell death induced by monoclonal antibody engagement of CD1d is associated with overexpression of proapoptotic Bax and mitochondrial membrane potential loss but it is caspase-activation independent; in addition, it requires the cytoplasmic tail but not the Tyr residue critical for lysosomal sorting of CD1d. Finally, anti-CD1d cooperates with antimyeloma agents in the killing of myeloma cells. Thus, this work provides evidence linking a novel function of CD1d in the regulation of cell death with tumor survival and progression in humans.