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Asthma in children exposed to cat allergen - new insights
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 Picture: 漏 Bayer Animal Health
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Cats are often claimed to cause asthma in children, and many allergologists recommend a cat-free household. But there are also controverse studies showing that animals in the household decrease the number of allergic reactions in children. This article gives an excellent overview over the possible reactions to cat allergens...
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Background: Although asthma is strongly associated with immediate hypersensitivity to indoor allergens, several studies have suggested that a cat in the house can decrease the risk of asthma. We investigated the immune response to cat and mite allergens, and asthma among children with a wide range of allergen exposure.
We did a population-based cross-sectional study of children (aged 12-14 years),some of whom had symptoms of asthma and bronchial hyper-reactivity. Antibodies to mite (Der f 1) and cat (Fel d 1) allergens measured by isotype (IgG and IgG4) specific radioimmunoprecipitation assays were compared with sensitisation and allergen concentrations in house dust.
226 children were recruited, 47 of whom had symptoms of asthma and bronchial hyper-reactivity. Increasing exposure to mite was associated with increased prevalence of sensitisation and IgG antibody to Der f 1. By contrast, the highest exposure to cat was associated with decreased sensitisation, but a higher prevalence of IgG antibody to Fel d 1.
Thus, among children with high exposure, the odds of sensitisation to mite rather than cat was 4路0 (99% CI 1路49-10路00). Furthermore, 31 of 76 children with 23碌g Fel d 1 at home, who were not sensitised to cat allergen had >125 units of IgG antibody to Fel d 1. Antibodies to Fel d 1 of the IgG4 isotype were strongly correlated with IgG antibody in both allergic and non-allergic children (r=0路84 and r=0路66, respectively). Sensitisation to mite or cat allergens was the strongest independent risk factor for asthma (p<0路001).
Exposure to cat allergen can produce an IgG and IgG4 antibody response without sensitisation or risk of asthma. This modified T-helper-2 cell response should be regarded as a form of tolerance and may be the correct objective of immunotherapy. The results may also explain the observation that animals in the house can decrease the risk of asthma.
Cats and immune responses-
Our results cast major doubts about whether changing prevalence of asthma and allergic disease can be explained simply by a shift in the balance of Th1 and Th2 responses` Asthma is strongly associated with immediate hypersensitivity to indoor allergens.
However, studies have suggested that a cat in the house can decrease the risk of asthma. Thomas Platts-Mills and colleagues measured the presence of antibodies to cat and mite allergens in 226 asthmatic children and compared the data with sensitisation and allergen concentrations in house dust.
Exposure to cat allergen, they found, could produce an IgG and IgG4 antibody response without sensitisation or risk of asthma.
This modified Th2 response should be regarded as a form of tolerance and may be the correct objective of immunotherapy.
Source: T Platts-Mills, J Vaughan, S Squillace, J Woodfolk, R Sporik (2001): Sensitisation, asthma, and a modified Th2 response in children exposed to cat allergen: a population-based cross-sectional study. In: Lancet 2001; 357: 752-56 Number 9258 10 March 2001
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