Murine models for the assessment of the contact sensitizing properties of chemicals rely on mouse ear swelling tests (Mest), which are not sensitive enough to detect weak sensitizers. The aim of the present study was to develop in mice an adjuvant-free Mest appropriate for in vivo detection of any type of sensitizer (weak to strong), and useful for in vitro assessment of contact sensitivity (CS). 3 haptens were tested: dinitrochlorobenzene (DNCB), para-phenylenediamine (pPD) and isoeugenol. We compared various protocols for induction of the CS reaction, differing by the site of induction, the number of applications and the concentrations of the 3 haptens. Comparison of the induction site for optimal CS reaction showed that, in Balb/c mice, the back was a better site of induction than the abdomen. Detection of the sensitizing properties of weak sensitizers (pPD, isoeugenol) was possible using an adjuvant-free protocol, provided that the induction phase comprised hapten applications on 3 consecutive days on the backs of animals. For DNCB, one application was sufficient to obtain optimal CS reaction. For all 3 haptens, a secondary response in vitro was obtained using semi-purified lymph node T cells from animals sensitized 5 days before with the optimized Mest. These results demonstrate that the Mest could be a useful experimental model for the study of all types of contact sensitizers.

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A derivation, more rigorous than hitherto, of the Relative Alkylation Index (RAI) as a quantifier of carrier protein haptenation in skin sensitization tests is presented. It is shown that the RAI, which is a composite parameter made up of dose, reactivity and lipophilicity terms, is likely to require a higher weighting for the reactivity term in the case of non-adjuvant tests than in the case of Freund's adjuvant-based tests. Methyl alkane-sulphonates, RSO3Me with R ranging from n-C6H13 to n-C16H33, were found to be skin sensitizers in a mouse ear swelling test, in agreement with published findings in a guinea-pig adjuvant model. A structure-activity relationship consistent with the published RAI model was observed whereby, in tests at fixed molar induction (0.1 mM) and challenge concentrations (0.025 mM), the level of sensitization response at first increased with increasing chain length of R, then showed a reversal of this trend at the highest chain length (R = n-C16H33). That this is a genuine 'over-load effect', as reported for several other series of compounds examined in guinea-pig adjuvant models, is indicated by the finding that on reducing the induction concentration for the R = n-C16H33 compound the sensitization response was increased. Alkyl and alkenyl methane-sulphonates, MeSO3R (R = n-C12H25, n-C18H37 and R = oleyl) did not give significant sensitization in the mouse ear test. Although they are chemically less reactive than methyl alkanesulphonates, these compounds are reported to be strong sensitizers in guinea-pig adjuvant tests and to fit a common quantitative sensitization-structure-dose relationship with the methyl alkanesulphonates.(ABSTRACT TRUNCATED AT 250 WORDS)