Relationship between dust mite allergen and human IgA in house dust samples

Previous investigators have mentioned that human IgA is found in house dust. IgA has also been reported to be present on human skin and hence in human dander. If human dander is the primary source of food for house dust mites, a relationship would be expected between IgA and dust mite allergen (Der f I) concentrations. We wished to learn whether IgA was consistently detectable in house dust and whether IgA and dust mite allergen concentrations were related. Dust samples were collected from the bedrooms of infants enrolled in a prospective study designed to evaluate the relationship between early allergen exposure and childhood allergic disease. One hundred eighty samples were studied: 50 samples were the initial samples collected from the first 50 infants enrolled, 120 samples were monthly samples obtained from 10 other homes, and 10 additional samples were randomly selected for extraction in a nonprotein containing buffer to determine the percentage of total extractable dust protein contributed by IgA. Finally, nine commercial house dust extracts were studied to learn whether they were similar to the dust samples from study houses. Enzyme linked immunosorbent assays (ELISAs) were used to measure human IgA, human secretory IgA (sIgA) and Der f I concentrations in all of the dust extracts. We found that IgA was consistently present in house dust samples ranging from 3.2 to 2,396 μg of IgA per gram of dust. A strong correlation (r = .90) was found between IgA and sIgA concentrations. IgA constituted 0.27% to 6.04% of the total protein in dust samples. Concentrations of IgA were significantly correlated with the density of home occupancy but not with Der f I concentrations. The ratio of Der f I to IgA showed a statistically significant (P = .025) seasonal variation while the seasonal variations in Der f I and IgA were not statistically significant (P > .13 for both). We concluded that human IgA is consistently present in house dust and that most of the IgA is of secretory origin. We also found that the ratio of IgA to Der f I varies seasonally.