Allergen-specific IgG1 provides parsimonious heritability estimates for atopy-associated immune responses to allergens.

Although serum total immunoglobulin E (IgE) is generally elevated in atopic conditions, it is an unreliable trait for dissecting the genetic and environmental components contributing to atopic immune responses, because it can be significantly confounded by demographic factors (age, gender, and race) and clinical status (atopic vs nonatopic). Allergen-specific IgE is a discontinuous trait present only in those with sensitivity to allergens. However, all people will produce allergen-specific immunoglobulin G1 (IgG1), which is elevated among those atopically sensitized to specific allergens. We screened 91 Caucasian nuclear families (N = 367) with medical histories of atopic diseases and used variance components analysis to compare heritability estimates for total IgE and IgG1 produced against the common major allergen from house dust mite Dermatophagoides pteronyssinus (Der p 1). An estimate of total IgE heritability was about 48%, although this was significantly confounded by age, gender, and clinical atopic status. In contrast, Der p 1-IgG1 demonstrated a significant inherited component of about 62% that was not influenced by age, gender, or clinical status. For genetic studies of atopic humoral responses, allergen-specific IgG1 may be a more reliable quantitative trait than serum IgE. Moreover, atopy is an inherited deregulation of immune responses to noninfectious antigens, involving antibody isotypes other than IgE.