The Pros and Cons of Airway Lining Fluid Composition Analysis
Authors: Mats W. Johansson
Journal: American Journal of Respiratory and Critical Care Medicine (2012)

Allergy and asthma are common conditions with genetic and environmental contributions (1). The prevalence of allergic diseases and asthma has increased during the last few decades (2). This increase in atopic diseases may be associated with prenatal and early-life exposure to triggering factors or, conversely, lack of exposure to protective factors (2, 3). Heredity from mothers or fathers may impact development of complex diseases differently. In this context, maternal atopy is more strongly associated with a child's risk to develop atopic disease than is paternal atopy (4–6), indicating a maternal effect on the child's immunological status.

The airway mucosa of the infant is exposed to the mother's milieu before birth and to allergens, pollutants, and microorganisms after birth. In their article in this issue of the Journal (pp. 275–280), Folsgaard and colleagues hypothesized that maternal and paternal atopy have a differential effect on cytokines and chemokines in the upper airway mucosa of healthy newborns (7). They studied 309 healthy subjects at 1 month of age. Subjects were recruited in Sjaelland (Zealand), Denmark, and enrolled in the new Copenhagen Prospective Study on Asthma in Childhood (COPSAC2010) cohort. Using a recently developed method (8), fluid lining mucosa of the upper airway was collected with strips of filter paper inserted into the nasal cavity. The filter had “wicking” properties, that is, efficient absorption of fluid with minimal adsorption of proteins to the paper. Thus, fluid proteins could be eluted from the paper into a defined volume, allowing the concentrations of 18 chemokines and cytokines to be estimated using multispot assays.

Results were analyzed in relation to parental atopy, defined as a history of physician-diagnosed asthma, hay fever, and/or atopic dermatitis, without an objective measurement such as IgE level or skin test for allergen-specific IgE (which is a limitation of the study). Principal component analysis indicated that in newborns with atopic mothers (with or without atopic fathers) as compared with nonatopic mothers (with or without atopic fathers), there was global down-regulation of the cytokines and chemokines. Many individual mediators (e.g., eotaxin-1, eotaxin-3, interferon γ, interleukin [IL]-1β, IL-13, monocyte chemotactic protein-1, monocyte chemotactic protein-4, and tumor necrosis factor-α) were decreased when subjected to t test. In contrast, newborns with atopic fathers (with or without atopic mothers) were similar to those with nonatopic fathers (with or without atopic mothers). Further and importantly, there was significant down-regulation in those with atopic mothers and nonatopic fathers compared with those with atopic fathers and nonatopic mothers. Overall, the data indicate that maternal, but not paternal, atopy is associated with mediator down-regulation in the upper airway mucosa of the infant. The authors interpret this finding as representing delayed maturation of the immune response that may put the infant at higher risk to develop atopy. Further follow-up would be needed to establish if there is indeed a link between down-regulated mediators in the upper airway mucosa lining fluid at 1 month and atopy later in life.

The minimally invasive sampling method would seem to have many advantages. In addition to minimizing discomfort, it avoids allergen challenge and nasal lavage, the confounding effect of the variable dilution of analytes during lavage, and the possibility that dilution may result in mediator concentrations lower than the detection limit of the assay (9, 10). Another strength is that the sample being studied is from a target organ of allergic disease rather than assaying cytokines and chemokines in stimulated cord or peripheral blood, as has been done previously in newborns (11–13). Further, use of principal component analysis is a strength. From variables or measurements that possibly are related, such analysis (14) extracts a few underlying, latent, uncorrelated variables, called principal components, which describe the systematic part of the variation. Principal component (PC) 1 describes the greatest part of data variation, PC2 the next greatest, and so on. In their data, the authors found that PC1 described 66% of the total variation and PC2 only a further 8%, and that there were significant differences in PC1 but not in PC2 among groups. The analyses indicated that all mediator concentrations are correlated and that the general down-regulation in newborns with atopic mothers mainly reflects one underlying inhibiting tendency.

In conclusion, the authors have made the novel observation that there is general down-regulation of cytokines and chemokines in the upper airway mucosa lining fluid in infants with symptomatic atopic mothers, likely mainly due to one underlying factor. The mechanism behind this maternal effect on the child's immunological status during pregnancy or first month of life remains unresolved. Possible explanations or hypotheses include exposure to allergens in utero (15), transfer of some factors or signals from the mother to the fetus, and/or a situation in which atopic mothers have different environmental or microbial exposures than nonatopic mothers during pregnancy or in the child's infancy. Allergic mothers may also avoid certain foods and have a different diet or nutrition than nonallergic mothers. Future studies seem warranted to address whether any of these possibilities explains the observed effect and to explore the significance of the effect.