Histamine-releasing factors, a heterogeneous group of different activities

Historic overview of allergy research in the Netherlands

Research in allergy has a long history in the Netherlands, although the relation with immunology has not always been appreciated. In many aspects Dutch researchers have made major contribution in allergy research. This ranges from the first characterization of house dust mite as an important allergen, the first characterization of human Th2 and Th1 T cell clones, to the development of diagnostic test systems. In this overview Aalberse and Knol have made an overview of the major contributions of Dutch immunologists in allergy.

Dimerization of translationally controlled tumor protein is essential for its cytokine-like activity

BACKGROUND

Translationally Controlled Tumor Protein (TCTP) found in nasal lavage fluids of allergic patients was named IgE-dependent histamine-releasing factor (HRF). Human recombinant HRF (HrHRF) has been recently reported to be much less effective than HRF produced from activated mononuclear cells (HRFmn).

METHODS AND FINDINGS

We found that only NH(2)-terminal truncated, but not C-terminal truncated, TCTP shows cytokine releasing activity compared to full-length TCTP. Interestingly, only NH(2)-terminal truncated TCTP, unlike full-length TCTP, forms dimers through intermolecular disulfide bonds. We tested the activity of dimerized full-length TCTP generated by fusing it to rabbit Fc region. The untruncated-full length protein (Fc-HrTCTP) was more active than HrTCTP in BEAS-2B cells, suggesting that dimerization of TCTP, rather than truncation, is essential for the activation of TCTP in allergic responses. We used confocal microscopy to evaluate the affinity of TCTPs to its putative receptor. We detected stronger fluorescence in the plasma membrane of BEAS-2B cells incubated with Del-N11TCTP than those incubated with rat recombinant TCTP (RrTCTP). Allergenic activity of Del-N11TCTP prompted us to see whether the NH(2)-terminal truncated TCTP can induce allergic airway inflammation in vivo. While RrTCTP had no influence on airway inflammation, Del-N11TCTP increased goblet cell hyperplasia in both lung and rhinal cavity. The dimerized protein was found in sera from allergic patients, and bronchoalveolar lavage fluids from airway inflamed mice.

CONCLUSIONS

Dimerization of TCTP seems to be essential for its cytokine-like activity. Our study has potential to enhance the understanding of pathogenesis of allergic disease and provide a target for allergic drug development.

Novel translationally controlled tumor protein homologue in the buccal gland secretion of Lampetra japonica

We have cloned a homologue of the translationally controlled tumor protein (TCTP) from the buccal gland of Lampetra japonica according to information from a cDNA library and primary analysis of expressed sequence tags. Sequence analysis of L. japonica TCTP showed that it had two signature regions of high sequence homology termed TCTP-1 and TCTP-2, respectively. TCTP is highly conserved in evolution. It showed more than 40% identification similarities with parasite TCTPs that had effect on immune responses of host. Phylogeny of 31 TCTP sequences showed that lamprey was closer to jawed vertebrates than to Amphioxus and was a sister group of gnathostomes. TCTP gene from L. japonica was expressed in a pET23b vector and purified by using His Bind affinity chromatography. Polyclonal antibody to recombinant protein was generated in New Zealand Rabbit. Immunoblot analysis to localize the recombinant protein in buccal gland secretion proves that recombinant TCTP is a secretion protein, which may be secreted through a non-classical secretion pathway. A characterization study shows that recombinant TCTP has histamine-releasing function in vitro. It mediated histamine release from rat basophilic leukemia (RBL-2H3) cells. TCTP links both the innate and the adaptive immune responses by modulating the secretion of cytokines from mast cells, basophils, eosinophils, and T and B lymphocytes. These may indicate a potential role of TCTP in the inflammatory process and immune regulation between L. japonica and host.

Immunology

The concept of forbidden foods that should not be eaten goes back to the Garden of Eden and apart from its religious meanings it may also have foreshadowed the concept of foods that can provoke adverse reactions. Thus we could say that allergic diseases have plagued mankind since the beginning of life on earth. The prophet Job was affected by a condition that following the rare symptoms described by the Holy Bible might be identified as a severe form of atopic dermatitis (AD). The earliest record of an apparently allergic reaction is 2621 B.C., when death from stinging insects was first described by hieroglyphics carved into the walls of the tomb of Pharaoh Menes depicting his death following the sting of a wasp. In 79 A.D., the death of the Roman admiral Pliny the Elder was ascribed to the SO₂-rich gases emanating from the eruption of Mount Vesuvius. Hippocrates (460–377 B.C.) was probably the first to describe how cow’s milk (CM) could cause gastric upset and hives, proposing dietetic measures including both treatment and prevention for CM allergy.

High-yield expression and purification of isotopically labeled norcoclaurine synthase, a Bet v 1-homologous enzyme, from Thalictrum flavum for NMR studies

The enzyme norcoclaurine synthase (NCS) found in the common meadow rue, Thalictrum flavum, and other plants shows sequence homology to members of the class 10 of pathogenesis related (PR 10) proteins that contains allergens such as the major birch pollen allergen Bet v 1, the major cherry allergen Pru av 1, and the major apple allergen Mal d 1. The enzyme is involved in the plant's secondary metabolism and is required for the production of bioactive secondary metabolites like morphine. Whereas the physiological function of PR 10 class allergens is still unknown, NCS activity has been studied in detail. Investigation of the structural properties of NCS by NMR spectroscopy can thus not only provide new information concerning the reaction mechanism of the enzyme, but is also expected to help clarify the long standing and heavily debated question on the physiological function as well as the reasons for the allergenic potential of members of this protein family. As the first important step towards the three-dimensional solution structure, we optimized expression of recombinant NCS in Escherichia coli and established an efficient purification protocol yielding high amounts of pure isotopically labeled active enzyme. The identity of NCS was confirmed by electrospray ionization mass spectrometry, and activity of the purified enzyme was determined by an assay detecting the radiolabeled reaction product. Spectroscopic analysis by NMR spectroscopy showed that the protein was properly folded with well defined tertiary structure.

Mast cells: multipotent local effector cells in atherothrombosis

Our understanding of the relationship between the proatherogenic activities of arterial mast cells (MCs) and the development of atherosclerotic lesions is advancing. Atherosclerosis is a chronic inflammatory disease in which cholesterol and other lipids of circulating low-density lipoprotein (LDL) particles accumulate both extracellularly and intracellularly in the innermost layer of the arterial wall, the intima. One prerequisite for the proatherogenic activity of the LDL particles is their retention and proteolytic modification within the extracellular matrix of the intima. Experimental studies with activated chymase-secreting MCs have provided us fundamental insights into the molecular mechanisms of these processes. High-density lipoprotein (HDL) particles, again, remove cholesterol from the intracellular stores and carry it back to the circulation. MC chymase and tryptase actively degrade HDL and thus generate functionally defective particles that are unable to initiate cholesterol efflux from the arterial wall. In advanced atherosclerotic plaques, the accumulated lipids are separated from the circulation by a collagenous cap. By inducing apoptosis of endothelial cells (ECs), subendothelial MCs may induce detachment of ECs from the cap (plaque erosion). Moreover, MCs may weaken the cap if they disturb local collagen turnover by inducing apoptosis of the collagen-secreting smooth muscle cells or when they promote collagen degradation by activating matrix metalloproteinases. Plaques with a weak cap are vulnerable to rupture. The exposed subendothelial tissue at eroded and ruptured sites of plaques triggers local development of a platelet-rich thrombus. As regulators of the collagen-induced platelet activation and fibrin formation/fibrinolysis, the MCs may retard or accelerate the growth of the plaque-associated thrombus and ultimately participate in the wound-healing response of the injured plaque. We propose that by promoting cholesterol accumulation and plaque vulnerability and by locally regulating hemostasis, MCs in atherosclerotic lesions have the potential to contribute to the clinical outcomes of atherosclerosis, such as myocardial infarction and stroke.

NMR solution structure of Ole e 6, a major allergen from olive tree pollen

Ole e 6 is a pollen protein from the olive tree (Olea europaea) that exhibits allergenic activity with a high prevalence among olive-allergic individuals. The three-dimensional structure of Ole e 6 has been determined in solution by NMR methods. This is the first experimentally determined structure of an olive tree pollen allergen. The structure of this 50-residue protein is based on 486 upper limit distance constraints derived from nuclear Overhauser effects and 24 torsion angle restraints. The global fold of Ole e 6 consists of two nearly antiparallel alpha-helices, spanning residues 3-19 and 23-33, that are connected by a short loop and followed by a long, unstructured C-terminal tail. Viewed edge-on, the structured N terminus has a dumbbell-like shape with the two helices on the outside and with the hydrophobic core, mainly composed of 3 aromatic and 6 cysteine residues, on the inside. All the aromatic rings lie on top of and pack against the three disulfide bonds. The lack of thermal unfolding, even at 85 degrees C, indicates a high conformational stability. Based on the analysis of the molecular surface, we propose five plausible epitopes for IgE recognition. The results presented here provide the structural foundation for future experiments to verify the antigenicity of the proposed epitopes, as well as to design novel hypoallergenic forms of the protein suitable for diagnosis and treatment of type-I allergies. In addition, three-dimensional structure features of Ole e 6 are discussed to provide a basis for future functional studies.

Adoptive transfer of alveolar macrophages abrogates bronchial hyperresponsiveness

Increasing evidence suggests that alveolar macrophages (AM) are involved in asthma pathogenesis. To better understand the role that these cells play, we investigated the capacity of AM from allergy-resistant rat, Sprague Dawley (SD), to modulate airway hyperresponsiveness of allergy-susceptible rat, Brown Norway (BN). AM of ovalbumin (OVA)-sensitized BN rats were eliminated by intratracheal instillation of liposomes containing clodronate. AM from OVA-sensitized SD rats were transferred into AM-depleted BN rats 24 h before allergen challenge. Airway responsiveness to methacholine was measured the following day. Instillation of liposomes containing clodronate in BN rats eliminated 85% AM after 3 d compared with saline liposomes. Methacholine concentration needed to increase lung resistance by 200% (EC200RL) was significantly lower in OVA-challenged BN rats (27.9 +/- 2.8 mg/ml) compared with SD rats (63.9 +/- 8.6 mg/ml). However, when AM from SD rats were transferred into AM-depleted BN rats, airway responsiveness (64.0 +/- 11.3 mg/ml) was reduced to the level of naïve rats (54.4 +/- 3.7 mg/ml) in a dose-dependent manner. Interestingly, transfer of AM from BN rats into SD rats did not modulate airway responsiveness. To our knowledge, this is the first direct evidence showing that AM may protect against the development of airway hyperresponsiveness.