e220 nFel d 2 Cat serum albumin

Allergens within Epidermals and Animal Proteins

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  • Latin name: Felis domesticus
  • Family: Felidae
  • Common names: Cat, Domestic cat
  • Source material: Serum albumin
Direct or indirect contact with animal allergens frequently causes sensitization. Animal allergens are major components in house dust.

Allergen Exposure

Geographical distribution
The Cat has been domesticated (probably from the small North African Wildcat Felis lybica) for around 5000 years. Cats have been greatly valued as destroyers of vermin, as well as for their ornamental qualities and their personalities as companion animals. Domestic Cats vary considerably in coat colour, quality and pattern, especially among the varieties bred for show. Cats occur in approximately 25% of Western households.
 
Environment
As well as in households and on farms, Cats are often found in a feral state in cities and rural environments. Rome has contained as many as a million feral Cats.
 
Allergens
Allergenic activity has been demonstrated in extracts of Cat dander and pelt (1-12) in serum (2, 3, 7, 13) in urine, (8, 9, 11, 13) and in saliva (9-13).
 
Various allergens have been isolated and characterised to date.
  • Fed 1 (formerly Cat 1 or Ag 4) (14-15)
  • Fel d 1.1
  • Fel d 1.2
  • Fel d 1.3
  • Fel d 2 (albumin) (16-17)  
  • Fel d 3, Cystatin, 11 kDa, a cysteine protease inhibitor (18)
Albumin (Fel d 2), a 65-69 kDa protein, is found in serum, dander and saliva. About 15%-25% of Cat-allergic individuals are sensitive to Cat albumin, and for a few patients this may be the predominant allergen (1, 19-23).
 
In a study that analyzed sera from 43 individuals with a history of cat allergy, 39.5% were positive to cat pelt, 37.5% to cat saliva, and 12% each to cat urine and serum. The cat pelt and saliva extracts contained allergen 1 (Fel d 1), but cat serum and cat urine collected by bladder puncture had no detectable levels of this allergen. A crossed immunoelectrophoresis/crossed radioimmunoelectrophoresis analysis failed to reveal any allergen in urine or serum that was not also present in the saliva or pelt preparations, although urine had two allergens not present in serum. When serum from a patient who had specific IgE antibodies to cat pelt, serum, saliva, and urine was tested by crossed radioimmunoelectrophoresis, it was determined that a total of six allergens were detectable in cat pelt, three in cat urine, and six in cat serum. Since cat serum contains no detectable cat allergen 1 (Fel d 1), it was concluded in this study that at least seven allergens derived from the cat are capable of binding to IgE antibodies in humans (24). 
 
Although more than 12 allergens have been identified, Fel d 1 is the most important one. Fel d 1, a 38 kDa protein, is found in hair, dander and saliva.

Potential Cross-Reactivity

Albumins from Cat, Dog and Horse share some epitopes that account for the cross-reactivity observed in around a third of patients sensitised to Cat, Dog and Horse, but more than 50% of specific IgE that cross-reacts among these 3 animals is directed to allergens other than albumin (25-26). Significant cross-reactivity has been reported between Cat hair and Dog dander in specific IgE inhibition studies, whereas saliva and urine were more species-specific (27).  Although a high degree of sequence homology exists among different animal albumins, a remarkable variability of IgE cross-reactivities has been observed, indicating that some patients are sensitised preferentially against certain albumins. Most of the patients allergic to albumins, however, reacted to Dog, Cat, and Horse albumin, which also bound a high percentage of albumin-specific IgE (28).
 
Some Cat-allergic individuals are likely to experience allergic symptoms following the consumption of Pork. Inhibition experiments showed that the spectrum of IgE reactivity to Cat serum albumin completely contained IgE reactivity to Porcine serum albumin. Sensitisation to Cat appears to be the primary event. Sensitisation to Cat serum albumin should be considered a useful marker of possible cross-sensitisation not only to Porcine serum albumin but also to other mammalian serum albumins (17).

Clinical Experience

IgE mediated reactions
Asthma, Occupational asthma, allergic rhinitis and allergic conjunctivitis are commonly induced by Cat allergens (29-30).  Domestic animals represent the second most important group of indoor air allergens after House Dust Mites (31). Sensitisation may occur even following unobserved exposure to Cat (32).  Cat dander allergens have even been found in dust storms (33).
 
Studies throughout the world, wherever Cats are common domestic pets, report high sensitisation to Cat dander. Sensitisation to Cat serum albumin has not been investigated to the same degree.
In Quebec, Canada, skin-specific IgE in 3371 consecutive patients revealed that the prevalence of sensitisation in atopic subjects to Cat hair epithelium was 76.5% (34).
 
In Vienna, Austria, skin- and serum-specific IgE determination led to the conclusion that Cat dander positivity was high in patients with respiratory allergy as well as normal individuals. The prevalence of sensitisation to Cat dander was highest in individuals with allergic rhinitis (44%) (35).  In 512 adults in southeastern France, serum-specific IgE to Cat was surprisingly low, with 0.9% of the group shown to have these antibodies (36).
 
Pet dander is one of the most common allergic triggers (17%) in the UK (37).  In Krakow, Poland, skin-specific IgE was positive for Cat dander in 11.4% of 311 children (38).  Cat dander was also shown to be an important allergen in Turkey (39).
 
In Sweden, serum IgE antibody assays on 165 children with respiratory symptoms confirmed that there was a high degree of sensitisation to Cat, Dog, and Birch in Northern Sweden. Cat and Dog allergens were present in almost all of the school samples. By contrast, Dust mite and Cockroach allergens were generally unmeasurable (40).
 
Compiled by Dr Harris Steinman, harris@zingsolutions.com

References:

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