How the immune system detects lipid antigens

Crosstalk within peripheral blood mononuclear cells mediates anti-inflammatory effects of n-3 PUFA-rich lipid emulsions in parenteral nutrition

BACKGROUND AND AIMS

Parenteral nutrition (PN) rich in n-6 and n-3 long-chain fatty acids is used in clinical practice for nourishing patients who are unable to receive adequate nutrition through their digestive systems. In this study, we compare the effect on inflammation of the commonly used lipid emulsions Omegaven (n-3-rich) and Intralipid (n-6-rich) in human peripheral blood mononuclear cells (PBMCs).

METHODS

PBMCs were treated with different doses of n-3-rich Omegaven and n-6-rich Intralipid and the immune cells were characterized by flow cytometry.

RESULTS

We show that incubation of PBMCs with n-3-rich Omegaven leads to an increase in expression of CD1d and CD86 in CD14+monocytes. At the same time, an increased number of NKT cells expressing cytotoxic T cell antigen 4 is observed, suggesting immunological synapse formation. Both CD14+monocytes and NKT cells showed an increase in IL-10 production and a reduction in the pro-inflammatory cytokines IFN-γ, TNF-α, and IL-4, which led to an increase in the number of FOXP3+T regulatory cells. In addition, we show that n-3-rich Omegaven reduces the expression of TNFα, IFNγ and IL-4 in CD4+T and CD8+T cells independent of the presented interaction between CD14+monocytes and NKT cells. The described mechanism of n-3 rich lipid emulsions was confirmed in PBMCs from patients with inflammatory bowel disease but not in colorectal cancer patients which seem to lack the interaction between CD14+monocytes and NKT cells.

CONCLUSIONS

These results show a mechanism for the beneficial effect of the n-3-rich Omegaven in patients with inflammatory conditions but questions its use in patients with cancer. Hence, our results may assist in choosing the best lipid emulsion for patients who require PN.

CD1: A Singed Cat of the Three Antigen Presentation Systems

Contrary to general view that the MHC Class I and II are the kapellmeisters of recognition and response to antigens, there is another big player in that part of immunity, represented by CD1 glycoproteins. In contrast to MHC Class I or II, which present peptides, CD1 molecules present lipids. Humans express five CD1 proteins (CD1a-e), four of which (CD1a-d) are trafficked to the cell surface, where they may display lipid antigens to T-cell receptors. This interaction may lead to both non-cognate and cognate T cell help to B cells, the latter eliciting anti-lipid antibody response. All CD1 proteins can bind a broad range of structurally different exogenous and endogenous lipids, but each shows a preference to one or more lipid classes. This unorthodox binding behavior is the result of elaborate architectures of CD1 binding clefts and distinct intracellular trafficking routes. Together, these features make CD1 system a versatile player in immune response, sitting at the crossroads of innate and adaptive immunity. While CD1 system may be involved in numerous infectious, inflammatory, and autoimmune diseases, its involvement may lead to opposite outcomes depending on different pathologies. Despite these ambiguities and complexity, CD1 system draws growing attention and continues to show glimmers of therapeutic potential. In this review, we summarize the current knowledge about CD1 proteins, their structures, lipid-binding profiles, and roles in immunity, and evaluate the role of CD1 proteins in eliciting humoral immune response.

Phospholipid analysis in sera of horses with allergic dermatitis and in matched healthy controls

Background

Lipids have become an important target for searching new biomarkers typical of different autoimmune and allergic diseases. The most common allergic dermatitis of the horse is related to stings of insects and is known as insect bite hypersensitivity (IBH) or summer eczema, referring to its recurrence during the summer months. This intense pruritus has certain similarities with atopic dermatitis of humans. The treatment of IBH is difficult and therefore new strategies for therapy are needed. Autoserum therapy based on the use of serum phospholipids has recently been introduced for horses. So far, serum lipids relating to these allergic disorders have been poorly determined. The main aim of this study was to analyse phospholipid profiles in the sera of horses with allergic dermatitis and in their healthy controls and to further assess whether these lipid profiles change according to the clinical status after therapy.

Methods

Sera were collected from 10 horses with allergic dermatitis and from 10 matched healthy controls both before and 4 weeks after the therapy of the affected horses. Eczema horses were treated with an autogenous preparation made from a horse’s own serum and used for oral medication. Samples were analysed for their phospholipid content by liquid chromatography coupled to a triple-quadrupole mass spectrometer (LC-MS). Data of phospholipid concentrations between the groups and over the time were analysed by using the Friedman test. Correlations between the change of concentrations and the clinical status were assessed by Spearman’s rank correlation test.

Results

The major phospholipid classes detected were phosphatidylcholine (PC), sphingomyelin (SM), phosphatidylinositol (PI) and phosphatidylethanolamine (PE). Eczema horses had significantly lower total concentrations of PC (p < 0.0001) and SM (p = 0.0115) than their healthy controls. After a 4-week therapy, no significant differences were found between the groups. Changes in SM concentrations correlated significantly with alterations in clinical signs (p = 0.0047).

Conclusions

Horses with allergic dermatitis have an altered phospholipid profile in their sera as compared with healthy horses and these profiles seem to change according to their clinical status. Sphingomyelin seems to have an active role in the course of equine insect bite hypersensitivity.

MHC and Evolution in Teleosts

Major histocompatibility complex (MHC) molecules are key players in initiating immune responses towards invading pathogens. Both MHC class I and class II genes are present in teleosts, and, using phylogenetic clustering, sequences from both classes have been classified into various lineages. The polymorphic and classical MHC class I and class II gene sequences belong to the U and A lineages, respectively. The remaining class I and class II lineages contain nonclassical gene sequences that, despite their non-orthologous nature, may still hold functions similar to their mammalian nonclassical counterparts. However, the fact that several of these nonclassical lineages are only present in some teleost species is puzzling and questions their functional importance. The number of genes within each lineage greatly varies between teleost species. At least some gene expansions seem reasonable, such as the huge MHC class I expansion in Atlantic cod that most likely compensates for the lack of MHC class II and CD4. The evolutionary trigger for similar MHC class I expansions in tilapia, for example, which has a functional MHC class II, is not so apparent. Future studies will provide us with a more detailed understanding in particular of nonclassical MHC gene functions.

Increased CD1D polymorphism: identification of two novel alleles, CD1D*03 and *04, in individuals from Morocco

Two novel CD1D alleles were identified in unrelated individuals from Morocco. They differ each from the common CD1D*01 allele by one nucleotide substitution in exon 2 resulting in one amino acid change in the G-ALPHA1-LIKE domain. According to the IMGT unique numbering for G domain, CD1D*03 has one nucleotide transition c136 > t in codon 46, with an arginine-to-cysteine amino acid change (R46 > C) in the D-STRAND, whereas CD1D*04 has one transition c98 > t in codon 33, with a threonine-to-methionine amino acid change (T33 > M) in the C-STRAND. This suggests that CD1D is more polymorphic than previously assumed.

Targeted delivery of mycobacterial antigens to human dendritic cells via Siglec-7 induces robust T cell activation

Lipids from mycobacteria can be presented to human T cells by group 1 CD1 Ag-presenting molecules (CD1a, CD1b, and CD1c). Group 1 CD1-restricted T cells are activated by lipid Ags presented by myeloid dendritic cells (DCs), after which they generate antibacterial effector functions, including IFN-γ secretion and cytolysis. Thus, mycobacterial lipids are being investigated as components of novel vaccines for mycobacterial infections. In this study we show that the mycobacterial lipid Ag C80 glucose-6-monomycolate can be delivered to human CD1b(+) DCs via targeted liposomal nanoparticles, leading to robust group 1 CD1-restricted activation of T cells. Targeting was achieved by decorating the liposomes with a high-affinity glycan ligand of sialic acid-binding Ig-like lectin (Siglec)-7, a siglec receptor expressed on DCs that mediates rapid endocytosis and transport of its cargo to lysosomes. An Ab to Siglec-7 completely blocked the binding of targeted liposomes to human monocyte-derived DCs (Mo-DCs), demonstrating their targeting specificity. Mo-DCs pulsed with targeted liposomes containing C80 glucose-6-monomycolate more potently activated a CD1b-restricted T cell line relative to Mo-DCs pulsed with free lipid Ag or antigenic liposomes without Siglec-7 ligand. These data suggest that the endocytic function of Siglec-7 can be exploited to deliver glycolipid Ags to their target cell and increase the efficiency of display to T cells.

Immune system targeting by biodegradable nanoparticles for cancer vaccines

The concept of therapeutic cancer vaccines is based on the activation of the immune system against tumor cells after the presentation of tumor antigens. Nanoparticles (NPs) have shown great potential as delivery systems for cancer vaccines as they potentiate the co-delivery of tumor-associated antigens and adjuvants to dendritic cells (DCs), insuring effective activation of the immune system against tumor cells. In this review, the immunological mechanisms behind cancer vaccines, including the role of DCs in the stimulation of T lymphocytes and the use of Toll-like receptor (TLR) ligands as adjuvants will be discussed. An overview of each of the three essential components of a therapeutic cancer vaccine - antigen, adjuvant and delivery system - will be provided with special emphasis on the potential of particulate delivery systems for cancer vaccines, in particular those made of biodegradable aliphatic polyesters, such as poly(lactic-co-glycolic acid) (PLGA) and poly-ε-caprolactone (PCL). Some of the factors that can influence NP uptake by DCs, including size, surface charge, surface functionalization and route of administration, will also be considered.

High-fat diet protects BB/OK rats from developing type 1 diabetes

BACKGROUND

It is well known that lipid metabolism plays an important role in the early stages of type 1 diabetes (T1D). For that reason, we examined factors that influence lipid metabolism of BioBreeding/Ottawa Kalsburg (BB/OK) rats that spontaneously develop an insulin-dependent T1D.

METHODS

BB/OK female rats were fed a high-fat diet during pregnancy (Ssniff R-Z + 10% tallow) and their progeny were also given this diet up to an age of 30 weeks (n = 55) or 4 weeks (n = 14) to study gene expression of Pparg, Fasn, Lep, Adipoq, Repin1, Rarres 2, and Glut4 in adipose tissue. Forty-two BB/OK rats fed the normal diet (Ssniff R-Z) during pregnancy and the observation period served as controls.

RESULTS

The high-fat diet significantly decreased diabetes frequency in BB/OK rats when compared with control rats (71 versus 95%, p = 0.002). Although this difference was also reflected in the male rats (68 versus 100%, p = 0.003), no significant variation was observed in female rats (73 versus 90%, p = 0.23). The high-fat diet resulted in significantly reduced mRNA expression of examined genes in subcutaneous adipose tissue, but not in visceral adipose tissue, except for Fasn and Repin1 expression.

CONCLUSIONS

A high-fat diet seems to protect BB/OK rats from T1D in a sex-specific manner. The data suggest that a high-fat diet might influence fat accumulation and/or fat metabolism and prevent T1D development in male rats, which is supported by changes in adipose tissue gene expression.

A naive-like population of human CD1d-restricted T cells expressing intermediate levels of promyelocytic leukemia zinc finger

Rare CD1d-α-galactosylceramide-specific T cells that do not express the invariant Vα24 chain of human NKT cells were recently identified after expansion in vitro with the lipid Ag, but their phenotype and frequency in vivo and lineage relationship with NKT cells could not be elucidated. By using a CD1d tetramer-based method to enrich these cells from fresh peripheral blood, we demonstrated their naive-like CD62L(high)CD45RO(-)CD4(+) phenotype and relatively high frequency of ∼10(-5) in several healthy individuals. Notably, these cells expressed the NKT lineage-specific transcription promyelocytic leukemia zinc finger (PLZF), indicating a developmental relationship with NKT cells and ruling out the possibility that they were conventional MHC-restricted T cells cross-reacting against CD1d-α-galactosylceramide. Although PLZF is known to direct the effector program of NKT cells, we show in this study that the naive-like cells expressed it at a significantly lower amount than NKT cells. Further, we present mouse studies demonstrating a sharp PLZF expression threshold requirement for induction of the effector phenotype. These findings directly demonstrate in vivo the existence of naive-like CD1d-restricted human T cells marked by intermediate levels of PLZF.

Lipoarabinomannan and related glycoconjugates: structure, biogenesis and role in Mycobacterium tuberculosis physiology and host-pathogen interaction

Approximately one third of the world's population is infected with Mycobacterium tuberculosis, the causative agent of tuberculosis. This bacterium has an unusual lipid-rich cell wall containing a vast repertoire of antigens, providing a hydrophobic impermeable barrier against chemical drugs, thus representing an attractive target for vaccine and drug development. Apart from the mycolyl–arabinogalactan–peptidoglycan complex, mycobacteria possess several immunomodulatory constituents, notably lipomannan and lipoarabinomannan. The availability of whole-genome sequences of M. tuberculosis and related bacilli over the past decade has led to the identification and functional characterization of various enzymes and the potential drug targets involved in the biosynthesis of these glycoconjugates. Both lipomannan and lipoarabinomannan possess highly variable chemical structures, which interact with different receptors of the immune system during host–pathogen interactions, such as Toll-like receptors-2 and C-type lectins. Recently, the availability of mutants defective in the synthesis of these glycoconjugates in mycobacteria and the closely related bacterium, Corynebacterium glutamicum, has paved the way for host–pathogen interaction studies, as well as, providing attenuated strains of mycobacteria for the development of new vaccine candidates. This review provides a comprehensive account of the structure, biosynthesis and immunomodulatory properties of these important glycoconjugates.

CD1a and CD1d genes polymorphisms in breast, colorectal and lung cancers

CD1 molecules might contribute to anti-tumor immune response by presentation of tumor-derived lipid and glycolipid antigens to T cells and NKT cells. Polymorphisms in CD1 genes have been suggested to modify ligand binding of CD1 molecules and thereby change the antigen presenting ability of these molecules. The aim of this study was to investigate the exon 2 polymorphisms of CD1a and CD1d in several high incident cancers in Iran. For this purpose, 201 female breast cancer patients and 207 healthy women, 64 lung cancer patients and 95 healthy individuals and 109 patients with colorectal cancer and 109 healthy controls were recruited to this study. Using PCR-SSP method, no significant correlation was found in genotype and allele frequencies of CD1a between all three studied groups and their control counterparts. Moreover, a dominant frequency of CD1d 01 (A) allele was observed in the majority of studied individuals. No significant association between the CD1 polymorphisms and prognostic factors in breast, lung and colorectal cancers was detected. Our results highlight the conserved nature of CD1 genes and may point to the immuoregulatory functions of CD1 molecules in cancer that can be exerted through fine tuning of NK, T and NKT cells.