Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
Individual mite allergens can be measured with enzyme-linked
immunosorbent assays (ELISA) or radioimmunoassays (RIA). Sandwich
radio- or enzyme immunoassays employ either rabbit polyclonal or mouse
monoclonal antibody for capture, and a second monoclonal antibody for
detection (see Fig. 25). These assays are more sensitive than RAST.
Those using monoclonal antibodies in particular have also the great
potential advantage of long-term reproducibility. Furthermore, ELISA
assays have been shown to be highly reproducible (e.g., Munir et al.,
1993; Van Strien et al., 1994) and can quantify antigen levels to less
than 1 ng/mg dust.
Immunochemical assays are highly specific and the results
obtained with these assays can be expressed in absolute units of a
defined protein by unit weight of dust or by unit area sampled. They
are suitable for large-scale surveys because they can be automated.
However, a sophisticated laboratory is required.
9.2.3.3 Guanine determination
The third possibility is the measurement of guanine, which is a
nitrogenous excretory product of arachnids, found in house dust. Since
mites are predominant among arachnids in house dust, determination of
guanine content in the dust is an indirect method for assessing mite
allergen levels. Analysis of guanine content is based on a colour
reaction between guanine and an azo compound (Le Mao et al., 1989;
Hoyet et al., 1991). The amounts of guanine can be measured
quantitatively on a weight/weight basis using a spectrophotometer, or
semiquantitatively using a commercially available test kit (Pauli et
al., 1995). The quantitative assay has been reported to demonstrate a
good correlation with the assay of Group 1 allergens (Platts-Mills et
al., 1992), whereas the semiquantitative test was found to be less
sensitive (Lau et al., 1990).
9.2.4 Mite allergens
Sampling strategies may vary depending on objectives but most
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