Horse serum proteins

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Code: e205
Latin name: Equus caballus
Source material: Serum
Family: Equidae
Common names: Horse, Domestic Horse
Direct or indirect contact with animal allergens frequently causes sensitisation.

Allergen Exposure

Geographical distribution
Except for a few feral populations, and one extremely endangered wild one (Przewalski's Horse), Horses are domesticated. Long used as a means of transportation, pleasure, work, and even war, Horses have been involved in much of human history. Domestic Horse breeds are numerous and highly various. Although little used for work today in developed countries, Horses are widely owned for recreational riding and show activities.
Horses are found in agricultural and recreational settings.
Unexpected exposure
Horsehair is encountered in antique furniture, and Horse meat is eaten in some countries in place of Beef. Horsehide is used in making baseballs and certain other leather goods.
At least 16 allergens have been isolated from Horse (1-4). Several allergens have been shown to be glycoproteins, including a 27 and a 31 kDa protein (5).
A number of allergens have been characterised:
  • Equ c 1, Mw 25 kDa, a lipocalin (6-10)
  • Equ c 2, Mw 16 kDa, a lipocalin (6, 8, 10-12)
  • Equ c 3 Mw 67 kD, albumin (Ag3) (10, 12)
  • Equ c 4, Mw 18.7 kDa (6, 12)
  • Equ c 5, Mw 16.7 kDa (6)
Various isoforms of Equ c 1 and Equ c 2 have been identified, including Equ c 2.0101 and Equ c 2.0102 (4) (11) . Both allergens have been cloned from the sublingual salivary glands and have also been found to be expressed in the liver and submaxillary salivary glands (7).
Already in early studies an important 67 kDa allergen has been isolated that was thought to be Horse albumin (13).

Potential Cross-Reactivity

In a study assessing the importance of albumin as a cross-reactive allergen in patients sensitised to Cat, Dog and Horse, 117 patients sensitised to Cat were tested for IgE reactivity using skin-specific IgE and RAST assays with Cat, Dog and Horse hair/dander extracts and their purified albumin extracts. Of these patients, 22% exhibited specific IgE to Cat albumin; 41% of patients sensitised to Cat were also sensitised to Dog and Horse. Of these patients, 21% had IgE antibodies to 3 albumins and 17% to 2. Specific IgE binding to Horse extract was inhibited in 30% of samples by its homologous albumin, and IgE binding to Cat and Dog extracts in almost 15% by their respective albumins. The study concluded that albumins from these three animals share some epitopes that account for the cross-reactivity observed in around 1/3 of patients sensitised to Cat, Dog and Horse. Nevertheless, more than 50% of specific IgE that cross-reacts among these 3 animals is directed to allergens other than albumin (14). Similar findings were documented in a second study (15).

Clinical Experience

IgE-mediated reactions
Horse allergy occurs among people who regularly handle Horses, either professionally or for recreational purposes, resulting in the induction or exacerbation of asthma, allergic rhinitis, allergic conjunctivitis and occupational asthma (16-22). Horse allergy has also been reported to result in angioedema, respiratory distress, and poorly controlled asthma (23).
In a study reviewing children seen for allergy to Horses over a period of 11 years (35 boys and 21 girls, 35 of them were under 10 years of age), the main clinical signs reported were ocular symptoms (36), asthma (30) and rhinopharyngitis (24). All the children had highly positive skin-specific IgE tests and 62% had specific IgE (class 3 and 4) and were polysensitised. In several children, the first symptoms occurred at the time of the first known contact with a Horse or Pony (24). Horse allergy has been reported to decrease with age (25).
Eosinophilic granuloma of the lung with sawdust and Horse protein hypersensitivity has been reported (26).
Other reactions
Contact urticaria from Horse saliva has been reported (27).
A high proportion of workers on a pure-bred Horse farm showed a positive skin response to Saccharopolyspora rectivirgula (51.6%), or showed the presence of precipitins to Acinetobacter calcoaceticus (32.3%). No significant relationship could be found between the presence of symptoms and positive allergy reactions, and the possibility of Organic Dust Toxic Syndrome occurring in a high proportion of the workers was suggested (28).
Farmer's Lung is a rural disease that can be caused by inhalation of airborne Thermophilic actinomycetes. Farmer's Lung occurred in an 11-year-old girl briefly exposed to this mould at a riding school (29).
Compiled by Dr Harris Steinman,


  1. Løwenstein H. Allergene von Katze, Hund, Rind und Pferd. Allergologie 1981;4:265
  2. Løwenstein H, Markussen B, Weeke B. Identification of allergens in extract of horse hair and dandruff by means of crossed radioimmunoelectrophoresis. Int Arch Allergy Appl Immunol 1976;51(1):38-47
  3. Markussen B, Loowenstein H, Weeke B. Allergen extract of horse hair and dandruff. Quantitative immunoelectrophoretic characterization of the antigens. Int Arch Allergy Appl Immunol 1976;51(1):25-37
  4. Bulone V, Rademaker GJ, Pergantis S, Krogstad-Johnsen T, Smestad-Paulsen B, Thomas-Oates J. Characterisation of horse dander allergen glycoproteins using amino acid and glycan structure analyses. a mass spectrometric method for glycan chain analysis of glycoproteins separated by two-dimensional electrophoresis. Int Arch Allergy Immunol 2000;123(3):220-7
  5. Johnsen, Thanh DB, Ly Q, Smestad Paulsen B, Wold JK. Further characterization of IgE-binding antigens in horse dander, with particular emphasis on glycoprotein allergens. Allergy 1996;51(9):608-13
  6. Goubran Botros H, Poncet P, Rabillon J, Fontaine T, Laval JM, David B. Biochemical characterization and surfactant properties of horse allergens. Eur J Biochem 2001;268(10):3126-36
  7. Gregoire C, Rosinski-Chupin I, Rabillon J, et al. cDNA cloning and sequencing reveal the major horse allergen Equ c1 to be a glycoprotein member of the lipocalin superfamily. J Biol Chem 1996;271(51):32951-9
  8. Mantyjarvi R, Rautiainen J, Virtanen T. Lipocalins as allergens. Biochim Biophys Acta 2000;1482(1-2):308-17
  9. Lascombe MB, Gregoire C, Poncet P, Tavares GA, Rosinski-Chupin I, Rabillon J, Goubran-Botros H, Mazie JC, David B, Alzari PM. Crystal structure of the allergen Equ c 1. A dimeric lipocalin with restricted IgE-reactive epitopes. J Biol Chem 2000;275(28):21572-7
  10. Dandeu JP, Rabillon J, Divanovic A, Carmi-Leroy A, David B. Hydrophobic interaction chromatography for isolation and purification of, the horse major allergen. J Chromatogr 1993;621(1):23-31
  11. Bulone V, Krogstad-Johnsen T, Smestad-Paulsen B. Separation of horse dander allergen proteins by two-dimensional electrophoresis. Molecular characterisation and identification of Equ c 2.0101 and Equ c 2.0102 as lipocalin proteins. Eur J Biochem 1998;253:202-211
  12. Goubran Botros H., Rabillon J., Grégoire C., David B., Dandeu J.P. Thiophilic absorption chromatography: purification of Equ c 2 and Equ c 3, two horse allergens from horse sweat. J Chromatogr 1998;B 710:57-65
  13. Fjeldsgaard BE, Paulsen BS. Comparison of IgE-binding antigens in horse dander and a mixture of horse hair and skin scrapings. Allergy 1993;48(7):535-41
  14. Cabanas R, Lopez-Serrano MC, Carreira J, Ventas P, Polo F, Caballero MT, Contreras J, Barranco P, Moreno-Ancillo A. Importance of albumin in cross-reactivity among cat, dog and horse allergens. J Investig Allergol Clin Immunol 2000;10(2):71-7
  15. Spitzauer S, Pandjaitan B, Soregi G, Muhl S, Ebner C, Kraft D, Valenta R,Rumpold H. IgE cross-reactivities against albumins in patients allergic to animals. J Allergy Clin Immunol 1995;96(6 Pt 1):951-9
  16. Romanski B, Montowska L, Wilewska T, Zbikowska M. Case of bronchial asthma caused by hypersensitivity to equine epidermis antigens (clinical and immunological analysis). [Polish] Wiad Lek 1975;28(12):1055-9
  17. Rudolph R, Meier-Duis H, Kunkel G, Staud RD, Stock U. Allergies to animal hair in diseases of the upper respiratory tract (author's transl). [German] Dtsch Med Wochenschr 1975;100(50):2557-61
  18. Berrens L, Koers WJ. Allergy to horse dander allergens. Clin Allergy 1978;8(3):311-2
  19. Chapman MD, Wood RA. The role and remediation of animal allergens in allergic diseases. J Allergy Clin Immunol 2001;107(3 Suppl):S414-21
  20. Leegaard J, Roth A. RAST in the diagnosis of hypersensitivity to horse allergens. A comparison with clinical history and in vivo tests. Clin Allergy 1977;7(5):455-64
  21. Bessot JC, Blaumeiser M, Kopferschmitt MC, Pauli G. Occupational asthma in an agricultural setting. [French] Rev Mal Respir 1996;13(3):205-15
  22. Krakowiak A, Szulc B, Palczynski C, Gorski P. Laboratory animals as a cause of occupational allergy. [Polish] Med Pr 1996;47(5):523-31
  23. Roberts G, Lack G. Horse allergy in children. BMJ 2000 Jul 29;321(7256):286-7
  24. Lelong M, Castelain MC, Bras C, Drain JP, Leonard JC, Robberecht MN, Libessart Y, Thelliez P, Miersman R. An outbreak of allergy to horses in children. A review of 56 recent cases. [French] Pediatrie 1992;47(1):55-8
  25. Eriksson NE, Holmen A. Skin prick tests with standardized extracts of inhalant allergens in 7099 adult patients with asthma or rhinitis: cross-sensitizations and relationships to age, sex, month of birth and year of testing. J Investig Allergol Clin Immunol 1996;6(1):36-46
  26. Girard JP, Bouzakoura C. Eosinophillic granuloma of the lung with sawdust and horse protein hypersensitivity. Clin Allergy 1974;4(1):71-8
  27. van der Mark S. Contact urticaria from horse saliva. Contact Dermatitis 1983;9(2):145
  28. Mackiewicz B, Prazmo Z, Milanowski J, Dutkiewicz J, Fafrowicz B. Exposure to organic dust and microorganisms as a factor affecting respiratory function of workers of purebred horse farms. [Polish] Pneumonol Alergol Pol 1996;64 Suppl 1:19-24
  29. Kristiansen JD, Lahoz AX. Riding-school lung? Allergic alveolitis in an 11-year-old girl. Acta Paediatr Scand 1991;80(3):386-8


As in all diagnostic testing, the diagnosis is made by the physican based on both test results and the patient history.