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  Discussion on Research Studies: Status of Insect Bite Hypersensitivity
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DrO

Posted on Tuesday, Dec 1, 2009 - 8:54 am:

These three papers add significantly to our understanding of the problem with Insect Bite Hypersensitivity but reinforces the problem with a accurate diagnosis.

Though often diagnosed on history and clinical signs alone, the difficult management decisions and sometimes poor results from management leads us to want to be sure we are diagnosing the right disease: is the problem one of controlling fly exposure or is the allergy is caused by something else?

Unfortunately these papers continue to find that blood and skin challenges are problematic in horses because so many healthy horses react to the insect salivary allergens. Purification of the salivary components and identification of the antigenic parts help us understand what is going on but still suffers the diagnostic problem of poor specificity with challenge. The paper suggests however that the test is sensitive so that a negative result to challenge with the purified salivary antigenic components in an allergic horse does help rule out insect bite hypersensitivity. With less purified insect salivary extracts even this has not been shown to be true.
DrO


Vet Immunol Immunopathol. 2009 Sep 24.
Insect bite hypersensitivity in the horse: Comparison of IgE-binding proteins in salivary gland extracts from Simulium vittatum and Culicoides nubeculosus.

Hellberg W, Mellor PS, Torsteinsdóttir S, Marti E.

Department of Clinical Research-VPH, Vetsuisse Faculty, University of Berne, Berne, Switzerland.

Insect bite hypersensitivity (IBH) is an IgE-mediated allergic dermatitis of horses caused by bites of insects such as Culicoides or Simulium spp. The aim of the present study was to compare the IgE-binding pattern of sea of IBH-affected horses to Culicoides nubeculosus and Simulium vittatum salivary gland extracts (SGE). Individual IgE responses to proteins of S. vittatum and C. nubeculosus AGEs were evaluated in 15 IBH-affected and three healthy horses on immunoblots. Fourteen out of the 15 IBH-affected but none of the healthy horses showed individual IgE binding patterns to seven and six main protein bands in C. nubeculosus and S. vittatum SGE, respectively. These 14 sera showed IgE-binding to proteins from SGE of both C. nubeculosus and S. vittatum, but they reacted with fewer protein bands derived from S. vittatum than from C. nubeculosus SGE. Sera showing IgE-binding to a 32 kDa band from C. nubeculosus always bound to a 32 kDa band from S. vittatum. Similarly, all sera binding to a 70 kDa band from C. nubeculosus reacted with a corresponding band in S. vittatum SGE. The 70 kDa bands from S. vittatum and C. nubeculosus were identified by mass spectrometry as heat shock protein-70-cognate-3.



Vet Immunol Immunopathol. 2009 Sep 23. [Epub ahead of print] Related Articles
Cloning of IgE-binding proteins from Simulium vittatum and their potential significance as allergens for equine insect bite hypersensitivity.

Schaffartzik A, Weichel M, Crameri R, Björnsdóttir TS, Price C, Rhyner C, Torsteinsdóttir S, Marti E.

Swiss Institute of Allergy and Asthma Research (SIAF), Obere Strasse 22, CH-7270 Davos, Switzerland; Division of Clinical Research, Department of Clinical Veterinary Medicine, Vetsuisse Faculty, University of Bern, Switzerland.

Insect bite hypersensitivity (IBH) is an allergic dermatitis of horses caused by bites of Culicoides and sometimes Simulium spp. The aim of this investigation was to identify Simulium allergens associated with IBH. A phage surface display cDNA library expressing recombinant Simulium vittatum salivary gland proteins was screened using sera of IBH-affected horses sensitized to S. vittatum salivary gland proteins as shown in immunoblot, resulting in the identification of seven cDNAs encoding IgE-binding proteins. The deduced amino acid sequences of these proteins showed sequence similarities to antigen 5 like protein (Sim v 1), to a serine protease inhibitor (Sim v 2), to two alpha-amylases (Sim v 3 and Sim v 4), and to three S. vittatum erythema proteins (SVEPs). The cDNA inserts were subcloned and expressed as [His](6)-tagged protein in Escherichia coli and purified using Ni(2+)-chelate affinity chromatography. Mice were immunised with the seven recombinant proteins and the antibodies tested against the recombinant proteins and salivary gland extract (SGE) of S. vittatum and Culicoides nubeculosus in immunoblot analyses. r-Sim v 1 specific mouse Abs recognized a band of about 32kDa in immunoblots of both S. vittatum and C. nubeculosus SGE, detectable also by serum IgE of IBH-affected horses. Preincubation of horse serum with r-Sim v 1 completely inhibited IgE binding to the 32kDa band demonstrating the presence of cross-reactive antigen 5 like proteins in both SGE. Determination of IgE levels against the r-Sim v proteins and crude S. vittatum extract by ELISA in sera from 25 IBH-affected and 20 control horses showed that IBH-affected horses had significantly higher IgE levels than controls against r-Sim v 1, 2, 3, 4 and S. vittatum extract, whereas the r-SVEP showed only marginal IgE binding. Further analyses showed that 60% of IBH-affected horses reacted to r-Sim v 1, suggesting that this could be a major allergen for IBH. Forty to twenty percent of the IBH-affected horses reacted with r-Sim v 2, 3 or 4. Combination of the results obtained with the 4 r-Sim v proteins showed that 92% of the IBH-affected but only 15% of the healthy horses had IgE levels against one or more of the 4 r-Sim v proteins. Seventy percent of the healthy horses had detectable IgE against S. vittatum extract, indicating a low specificity of the detection system used. Optimization of the ELISA system will be required to determine reliable cut-off values for the IBH-related allergens. Their in vivo relevance needs to be carefully assessed.


Vet Immunol Immunopathol. 2009 Sep 23.
Sensitization of skin mast cells with IgE antibodies to Culicoides allergens occurs frequently in clinically healthy horses.

Wagner B, Miller WH Jr, Erb HN, Paul Lunn D, Antczak DF.

Department of Population Medicine and Diagnostic Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA.

IgE antibodies are mediators of mast cell degranulation during allergic diseases. The binding of IgE to its high-affinity IgE receptor on mast cell surfaces is called "sensitization" and precedes the development of clinical allergy. Previously, intradermal injection of anti-IgE or the anti-IgG(T) antibody CVS40 induced immediate skin reactions in horses. This suggested that both IgE and IgG(T) sensitize equine skin mast cells. Here, we investigated sensitization to allergen and with IgE or IgG(T) in clinically healthy horses of different age groups. In addition, immediate skin reactions to Culicoides were determined by intradermal testing in non-allergic horses. A total of 14% of the young horses 1-3 years old and 38% of the adult animals showed skin reaction to Culicoides allergen extract. Sensitization with IgE and IgG(T) was evaluated in skin mast cells and peripheral blood basophils to determine whether sensitization with IgG(T) preceded that with IgE in young horses. Anti-IgE stimulated immediate skin reactions in 18 of 21 young horses, but only 7 of them reacted to the anti-IgG(T) antibody CVS40. The equine IgG(T) fraction is composed of IgG3 and IgG5. We used several newly developed monoclonal antibodies to IgG3 and IgG5 for intradermal testing to improve our understanding about the mast cell reaction induced by the anti-IgG(T) antibody CVS40. None of these antibodies induced a skin reaction in young or adult horses. To determine sensitization with IgE in neonates and foals at 6 and 12 weeks of age an in vitro histamine release assay was performed using peripheral blood cells. The histamine concentration released by anti-IgE stimulation from foal basophils increased between birth and 12 weeks of age, while almost no histamine release was observed after anti-IgG(T) treatment of the cells. In summary, IgE was the major immunoglobulin involved in the sensitization of mast cells and basophils in horses at various ages. IgG(T) antibodies did not play a major role in the activation of mast cells or basophils in young horses and their role in the sensitization of adult horses remains unclear. Sensitization to Culicoides allergen in the absence of clinical disease was frequently found in horses of all age groups. Because many clinically healthy horses developed skin reactions to this allergen, sensitization results are useful to diagnose Culicoides-induced allergy only in horses with allergic conditions.
Member:
gramsey1

Posted on Thursday, Dec 3, 2009 - 6:09 pm:

Interesting. I get bit by the flies that bite our horses as a matter of routine. Usually, I have the normal pain and itch reaction. Once in awhile, maybe once or twice a season, I have a very strong reaction, swelling and pain to the point that inflammation in joints near the bite can reduce range of motion. This year a bite near my elbow resulted in swelling that resulted in joint pain that persists today, many weeks after the swelling and acute pain subsided.
One must wonder if our equine partners can experience the same variation in response.
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