beta-(1,3)-Glucan exposure assessment by passive airborne dust sampling and new sensitive immunoassays

Abstract

Associations between house dust-associated beta-(1,3)-glucan exposure and airway inflammatory reactions have been reported, while such exposures in early childhood have been suggested to protect against asthma and wheezing. Most epidemiological studies have used reservoir dust samples and an inhibition enzyme immunoassay (EIA) for beta-(1,3)-glucan exposure assessment. The objective of this study was to develop inexpensive but highly sensitive enzyme immunoassays to measure airborne beta-(1,3)-glucans in low-exposure environments, like homes. Specificities of available anti-beta-(1,3)-glucan antibodies were defined by direct and inhibition experiments. Three suitable antibody combinations were selected for sandwich EIAs. beta-(1,3)-Glucans in passive airborne dust collected with an electrostatic dust fall collector (EDC) and floor dust from seven homes were measured with the three EIAs. Floor dust samples were additionally analyzed in the inhibition EIA. The sandwich EIAs were sensitive enough for airborne glucan measurement and showed different specificities for commercial glucans, while the beta-(1,3)-glucan levels in house dust samples correlated strongly. The feasibility of measuring glucans in airborne dust with the recently introduced EDC method was further investigated by selecting the most suitable of the three EIAs to measure and compare beta-(1,3)-glucan levels in the EDC and in floor and actively collected airborne dust samples of the previously performed EDC validation study. The EDC beta-(1,3)-glucan levels correlated moderately with beta-(1,3)-glucans in actively collected airborne dust and floor dust samples, while the glucan levels in the airborne dust and floor dust samples did not correlate. The combination of the newly developed beta-(1,3)-glucan sandwich EIA with EDC sampling now allows assessment in large-scale population studies of exposure to airborne beta-(1,3)-glucans in homes or other low-exposure environments.

FIG. 1.

Reactivities of antibodies to different coated glucans. Reactivity is expressed as 1,000 divided by the coating concentration (μg/ml) that is needed to achieve an OD of 1. Starting reactions not yet reaching an OD of <1 at 16 μg/ml were assigned a c_{OD = 1} of 32 μg/ml, while glucans not showing any reactivity at 16 μg/ml were assigned a c_{OD = 1} of 1,000. BAK, baker's yeast glucan; BAR, barley glucan; CUR, curdlan; LAM, laminarin; LIC, lichenan; OAT, oat glucan; PAC, pachyman; PAR, paramylon; PUL, pullulan; PUS, pustulan; SCH, schizophyllan; SCL, scleroglucan; XYL, xyloglucan. (A) Polyclonal rabbit anti-laminarin IgG (U1); (B) biotinylated monoclonal mouse antilaminarin IgG (B2); (C) anti-β-(1,3)-(1,6)-glucan mouse monoclonal IgM (P1); (D) anti-scleroglucan rabbit polyclonal Ig (P2).

FIG. 2.

Reactions of the 13 glucans in sandwich EIAs. See the legend to Fig. 1 for abbreviations of the glucans. (A) U1B2; (B) P1U1; (C) P1B2. Glucans showing reactions at an OD of <0.2 at 100 μg/ml (*) are not presented.

FIG. 3.

Comparison of glucan levels measured by different dust sampling methods. (A) Active airborne dust sampling versus EDC; (B) floor dust sampling versus EDC; (C) active airborne dust sampling versus floor dust sampling.