Heme Oxygenase-1 Induction by Blood-Feeding Arthropods Controls Skin Inflammation and Promotes Disease Tolerance.

Hematophagous vectors lacerate host skin and capillaries to acquire a blood meal, resulting in leakage of red blood cells (RBCs) and inflammation. Here, we show that heme oxygenase-1 (HO-1), a pleiotropic cytoprotective isoenzyme that mitigates heme-mediated tissue damage, is induced after bites of sand flies, mosquitoes, and ticks. Further, we demonstrate that erythrophagocytosis by macrophages, including a skin-residing CD163+CD91+ professional iron-recycling subpopulation, produces HO-1 after bites. Importantly, we establish that global deletion or transient inhibition of HO-1 in mice increases inflammation and pathology following Leishmania-infected sand fly bites without affecting parasite number, whereas CO, an end product of the HO-1 enzymatic reaction, suppresses skin inflammation. This indicates that HO-1 induction by blood-feeding sand flies promotes tolerance to Leishmania infection. Collectively, our data demonstrate that HO-1 induction through erythrophagocytosis is a universal mechanism that regulates skin inflammation following blood feeding by arthropods, thus promoting early-stage disease tolerance to vector-borne pathogens.

Antigenic and Substrate Preference Differences between Scorpion and Spider Dermonecrotic Toxins, a Comparative Investigation.

The Hemiscorpius lepturus scorpion and brown spider Loxosceles intermedia represent a public health problem in Asia and America, respectively. Although distinct, these organisms contain similar toxins responsible for the principal clinical signs of envenomation. To better understand the properties of these toxins, we designed a study to compare recombinant Heminecrolysin (rHNC) and rLiD1, the major phospholipase D toxins of scorpion and spider venom, respectively. Using a competitive ELISA and a hemolytic inhibition test, we come to spot a cross reaction between scorpion and spider venoms along with an epitopic similarity between rHNC and rLiD1 associated with neutralizing antibodies. Results show that the ability of the rHNC to hydrolyze lysophosphatidylcholine (LPC) is equivalent to that of rLiD1 to hydrolyze sphingomyelin and vice-versa. rHNC exclusively catalyze transphosphatidylation of LPC producing cyclic phosphatidic acid (cPA). The in-silico analysis of hydrogen bonds between LPC and toxins provides a possible explanation for the higher transphosphatidylase activity of rHNC. Interestingly, for the first time, we reveal that lysophosphatidic acid (LPA) can be a substrate for both enzymes using cellular and enzymatic assays. The finding of the usage of LPA as a substrate as well as the formation of cPA as an end product could shed more light on the molecular basis of Hemiscorpius lepturus envenomation as well as on loxoscelism.

Insect venom phospholipases A1 and A2: Roles in the envenoming process and allergy.

Insect venom phospholipases have been identified in nearly all clinically relevant social Hymenoptera, including bees, wasps and ants. Among other biological roles, during the envenoming process these enzymes cause the disruption of cellular membranes and induce hypersensitive reactions, including life threatening anaphylaxis. While phospholipase A2 (PLA2) is a predominant component of bee venoms, phospholipase A1 (PLA1) is highly abundant in wasps and ants. The pronounced prevalence of IgE-mediated reactivity to these allergens in sensitized patients emphasizes their important role as major elicitors of Hymenoptera venom allergy (HVA). PLA1 and -A2 represent valuable marker allergens for differentiation of genuine sensitizations to bee and/or wasp venoms from cross-reactivity. Moreover, in massive attacks, insect venom phospholipases often cause several pathologies that can lead to fatalities. This review summarizes the available data related to structure, model of enzymatic activity and pathophysiological roles during envenoming process of insect venom phospholipases A1 and -A2.

Lutzomyia longipalpis Saliva Induces Heme Oxygenase-1 Expression at Bite Sites.

Sand flies bite mammalian hosts to obtain a blood meal, driving changes in the host inflammatory response that support the establishment of Leishmania infection. This effect is partially attributed to components of sand fly saliva, which are able to recruit and activate leukocytes. Our group has shown that heme oxygenase-1 (HO-1) favors Leishmania survival in infected cells by reducing inflammatory responses. Here, we show that exposure to sand fly bites is associated with induction of HO-1 in vivo. Histopathological analyses of skin specimens from human volunteers experimentally exposed to sand fly bites revealed that HO-1 and Nrf2 are produced at bite sites in the skin. These results were recapitulated in mice ears injected with a salivary gland sonicate (SGS) or exposed to sand fly bites, indicating that vector saliva may be a key factor in triggering HO-1 expression. Resident skin macrophages were the main source HO-1 at 24-48 h after bites. Additionally, assays in vivo after bites and in vitro after stimulation with saliva both demonstrated that HO-1 production by macrophages was Nrf2-dependent. Collectively, our data demonstrates that vector saliva induces early HO-1 production at the bite sites, representing a major event associated with establishment of naturally-transmitted Leishmania infections.

Impact of age and heterophilic interference on the basal serum tryptase, a risk indication for anaphylaxis, in 1,092 dermatology patients.

A raised baseline serum tryptase is a risk indicator for anaphylactic reactions, especially in patients with hymenoptera venom allergy. Borderline elevations (> 11.4 µg/l) occur frequently and may necessitate invasive diagnostic procedures to rule out systemic mastocytosis. We retrospectively analysed 1,092 non-mastocytotic patients from our general dermatology clinic with respect to age- and gender-associated effects and investigated the impact of heterophilic antibody interference on the tryptase assay. The results were stratified by gender and five age classes. Sera with raised tryptase (n = 106) were re-tested after pre-incubation with Heterophilic Blocking Tubes (HBT(®), Scantibodies Laboratory; Santee, CA, USA). A significant increase in baseline tryptase was observed with increasing age. Incubation with HBT(®) caused a decline of more than 50% in only one case. In conclusion, older patients showed significantly higher serum tryptase levels and heterophilic interference was of subordinate relevance.

Basal serum tryptase as risk assessment for severe Hymenoptera sting reactions in elderly.

BACKGROUND: Epidemiologic studies suggest that elderly people are more prone to develop severe anaphylactic reactions. However, the exact cause for this phenomenon remains unclear. AIMS OF THE STUDY: To study the role of the serum tryptase as a diagnostic parameter for individual risk evaluation and its impact on the severity of allergic reactions in elderly people. METHODS: Two hundred and seventy-four consecutive patients visiting the Department of Dermatology, Tübingen, Germany, who were diagnosed with honeybee or wasp venom allergy, were included in the study. RESULTS: Sting reaction severity increased with increased age and tryptase levels (P = 0.001 and P = 0.0003, respectively). Furthermore, we find not only a general increment in tryptase levels in elderly people (P = 0.0001) but also a continuous increase in tryptase concentrations even below the cut-off (11.4 microg/l) with increasing age (P = 0.0026). CONCLUSIONS: Our data confirm serum tryptase as a risk factor for severe anaphylactic reaction to hymenoptera stings. Furthermore, we give first evidence that basal serum tryptase levels increase continuously with age and being an indicator for either increased mast cell load or reactivity this can at least partly be responsible for the observed aggravated allergic reactions in elderly people. As those patients are at increased risk for life-threatening anaphylactic reactions, it should be considered to adjust VIT especially in elderly patients with elevated tryptase levels as recommended for patients with mastocytosis by increasing venom doses during VIT and by considering its life-long continuation.

Elevated basal serum tryptase and hymenoptera venom allergy: relation to severity of sting reactions and to safety and efficacy of venom immunotherapy.

BACKGROUND: Mastocytosis and/or elevated basal serum tryptase may be associated with severe anaphylaxis. OBJECTIVE: To analyse Hymenoptera venom-allergic patients with regard to basal tryptase in relation to the severity of sting reactions and the safety and efficacy of venom immunotherapy. METHODS: Basal serum tryptase was measured in 259 Hymenoptera venom-allergic patients (158 honey bee, 101 Vespula). In 161 of these (104 honey bee, 57 Vespula), a sting challenge was performed during venom immunotherapy. RESULTS: Nineteen of the 259 patients had an elevated basal serum tryptase. Evidence of cutaneous mastocytosis as documented by skin biopsy was present in 3 of 16 patients (18.8%). There was a clear correlation of basal serum tryptase to the grade of the initial allergic reaction (P<0.0005). Forty-one of the 161 sting challenged patients reacted to the challenge, 34 to a bee sting and 7 to a Vespula sting. Thereof, 10 had an elevated basal serum tryptase, i.e. 1 (2.9%) of the reacting and 2 (2.9%) of the non-reacting bee venom (BV) allergic individuals, as compared to 3 (42.9%) of the reacting and 4 (8%) of the non-reacting Vespula venom-allergic patients. Thus, there was a significant association between a reaction to the sting challenge and an elevated basal serum tryptase in Vespula (chi2=6.926, P<0.01), but not in BV-allergic patients. Systemic allergic side-effects to venom immunotherapy were observed in 13.9% of patients with normal and in 10% of those with elevated basal serum tryptase. CONCLUSIONS: An elevated basal serum tryptase as well as mastocytosis are risk factors for severe or even fatal shock reactions to Hymenoptera stings. Although the efficacy of venom immunotherapy in these patients is slightly reduced, most of them can be treated successfully. Based on currently available data, lifelong treatment has to be discussed in this situation.

Elevated serum enzymes in patients with wasp/bee sting and their clinical significance.

Seventeen patients who had been admitted to hospital for wasp/bee sting were studied. Mild pyrexia was encountered in 7 patients, rash/urticaria in 3, angioneurotic oedema in 2, oliguria in 2, microscopic haematuria and albuminuria in 3, transient hypotension in 1. However, there were frequent elevations of serum glutamic-oxaloacetic transaminase (9 out of 17 patients), serum creatine phosphokinase (14 out of 17 patients) and serum lactate dehydrogenase (8 out of 14 patients), indicating presence of damage to muscle fibres. This was confirmed by the histological findings of a muscle-biopsy from the most severe case. Elevation of serum glutamic-pyruvic transaminase was found in 6, and elevation of serum isocitrate dehydrogenase in 5 out of 14 patients, suggesting presence of liver damage. The above enzyme elevations appeared short-lived except in the clinically most severe patient (case 9) who developed acute tubular necrosis. All patients except the latter suffered no clinical sequelae and there was no correlation between their clinical condition and the presence or degree of elevations of serum enzymes.