The Journal of Allergy and Clinical Immunology
Volume 125, Issue 3 , Pages 765-766, March 2010

Reply

National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC

published online 08 February 2010.

Article Outline

 

To the Editor:

Dr Brenna1 raises several important issues in his commentary. In epidemiologic studies, selection bias and lack of generalizability are not uncommon concerns. Study findings can be influenced by self-selection (ie, the healthy worker effect), especially in cross-sectional occupational studies. Studies of farming populations, however, have provided a unique opportunity to study the role of environmental factors in the development of atopic disorders. In the study by Mandhane et al,2 the longitudinal data were derived from a large, unselected, population-based cohort, which is one of the major strengths of the work. Indeed, the authors found no signs of selection bias in their study.

We acknowledge that pet ownership is not a very good surrogate for pet allergen exposures. In particular, personal allergen exposure can be highly variable, both spatially and temporally, because exposure levels are influenced by several factors, including the proximity of the source, reservoir concentration of allergen, nature of the source, and behavioral factors (eg, activity levels).3 Although homes may be the primary sites of exposure, exposure to cat and dog allergens is not limited to residential environments; both allergens are passively transported from one environment to another.4 However, the presence of indoor pets, cats and/or dogs, has been shown to be the strongest predictor of high pet allergen levels in homes.5

The hygiene hypothesis that was proposed as a potential explanation for time trends in allergic disease has remained a subject of intense debate over recent decades.6 Although the hypothesis has stimulated a substantial amount of research, the underlying etiologic mechanisms that confer protection against developing atopy are not completely understood. Nonetheless, there is increasing evidence to support that exposure to microbial infections in early life, as well as exposure to noninfectious microorganisms and microbial components, can influence innate and adaptive immune responses.7 Not only are cats and dogs sources of allergens, but also their presence has also been associated with other potential immunomodulatory agents, including endotoxin and other bacterial products.8, 9 It is therefore not surprising that exposure to cats and dogs in the home might modify immune system development. Exposure to pet allergens and microbial stimuli may have independent effects, or they may operate in an interactive manner. For example, studies have shown that cat-induced tolerance (modified TH2 response) is allergen-specific and cannot be explained by increased exposure to endotoxin.9 It is likely that gene-environment interactions also play an important role in the pathogenesis of allergic disorders. Emerging research suggests that an individual's response to microbial or other environmental exposures depends on genetic polymorphisms that alter immune responses to environmental stimuli.7

Although the findings reported by Mandhane et al2 are intriguing, further research is needed to elucidate the complex relationships between atopy and environmental exposures, including exposures to cats and dogs.

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References 

  1. Brenna OV. Cats and dogs: An attractive remedy versus atopy?. J Allergy Clin Immunol. 2010;125:765
  2. Mandhane PJ, Sears MR, Poulton R, Greene JM, Lou WYW, Taylor DR, et al. Cats and dogs and the risk of atopy in childhood and adulthood. J Allergy Clin Immunol. 2009;124:745–750
  3. O'Meara T, Tovey E. Monitoring personal allergen exposure. Clin Rev Allergy Immunol. 2000;18:341–395
  4. Salo PM, Sever ML, Zeldin DC. Indoor allergens in school and day care environments. J Allergy Clin Immunol. 2009;124:185–192
  5. Arbes SJ, Cohn RD, Yin M, Muilenberg ML, Friedman W, Zeldin DC. Dog allergen (Can f 1) and cat allergen (Fel d 1) in US homes: results from the National Survey of Lead and Allergens in Housing. J Allergy Clin Immunol. 2004;114:111–117
  6. Strachan DP. Family size, infection and atopy: the first decade of the “hygiene hypothesis.”. Thorax. 2000;55(suppl 1):S2–S10
  7. von Mutius E. Allergies, infections and the hygiene hypothesis—the epidemiological evidence. Immunobiology. 2007;212:433–439
  8. Bufford JD, Reardon CL, Li Z, Roberg KA, DaSilva D, Eggleston PA, et al. Effects of dog ownership in early childhood on immune development and atopic diseases. Clin Exp Allergy. 2008;38:1635–1643
  9. Platts-Mills JA, Custis NJ, Woodfolk JA, Platts-Mills TA. Airborne endotoxin in homes with domestic animals: implications for cat-specific tolerance. J Allergy Clin Immunol. 2005;116:384–389

 Supported by the Intramural Research Program of the NIH, National Institute of Environmental Health Sciences (Z01 ES025041).

 Disclosure of potential conflict of interest: The authors have declared that they have no conflict of interest.

PII: S0091-6749(09)01728-X

doi:10.1016/j.jaci.2009.11.012

Refers to article:

  • Cats and dogs: An attractive remedy versus atopy? , 08 February 2010

    Oreste V. Brenna
    The Journal of Allergy and Clinical Immunology March 2010 (Vol. 125, Issue 3, Page 765)

The Journal of Allergy and Clinical Immunology
Volume 125, Issue 3 , Pages 765-766, March 2010

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