THE MOUSE IGE TEST FOR THE IDENTIFICATION OF POTENTIAL CHEMICAL RESPIRATORY ALLERGENS - CONSIDERATIONS OF STABILITY AND CONTROLS

The mouse IgE test is a novel approach to the predictive identificatio n of chemicals that have the potential to cause sensitization of the r espiratory tract. The method is based upon measurement of induced chan ges in the serum concentration of IgE in BALB/c strain mice following topical exposure to the test chemical. The investigations described he re were undertaken to examine the stability of the assay, to evaluate the utility of trimellitic anhydride (TMA) and 2,4-dinitrochlorobenzen e (DNCB) as, respectively, positive and negative controls for use in t he test and to consider criteria for the classification of chemicals a s potential respiratory allergens based upon changes induced in serum IgE concentration. On the basis of fifteen independent experiments it was found that, while there was some intra- and inter-test variability with respect to absolute concentrations of IgE measured in the sera o f individual mice, the relative pattern of reactivity observed followi ng treatment of mice with TMA, DNCB or with vehicle (4:1 acetone:olive oil) alone remained consistent. In each experiment treatment with TMA provoked a very substantial increase in serum IgE relative to vehicle controls. In no instance did exposure of mice to DNCB cause an increa se in the concentration of serum IgE, and in some instances treatment with this chemical resulted in reduced IgE levels. In a parallel serie s of experiments it was found that serum IgE concentrations in vehicle -treated mice were comparable with those found in the serum of untreat ed animals. It is concluded that the differential ability of chemicals to induce changes in the concentration of serum IgE in BALB/c mice is a stable phenomenon. It is recommended that, in practice, TMA and DNC B should be incorporated in mouse IgE tests as, respectively, positive and negative controls. Finally, it is proposed that activity in the t est is assessed as a function of induced changes in serum IgE levels r elative to concurrent vehicle controls, rather than by reference to hi storical normal range values.