Allergy-inducing nickel concentration is lowered by lipopolysaccharide at both the sensitization and elicitation steps in a murine model.

BACKGROUND: Nickel (Ni) is the major cause of contact allergy. We previously found that lipopolysaccharide (LPS, a cell-surface component of gram-negative bacteria) markedly promotes Ni allergy in a murine model. Establishing the minimum concentration or amount of Ni needed to induce allergic responses may help us to prevent or reduce such responses.
OBJECTIVES: Using the above murine model, we examined the influence of LPS on the minimum allergy-inducing concentrations of Ni (Ni-MAICs) at the sensitization step and at the elicitation step.
METHODS: BALB/c mice were sensitized by intraperitoneal injection of a mixture containing various concentrations of LPS and NiCl(2). Ten days later, their ear pinnas were challenged intradermally with a mixture containing various concentrations of LPS and NiCl(2), and ear swelling was measured.
RESULTS: Without LPS, the Ni-MAICs at the sensitization and elicitation steps were around 1×10(-2) mol L(-1) and 1×10(-5) mol L(-1) , respectively. Sensitization with NiCl(2) + LPS did not alter the value at elicitation. Surprisingly, LPS markedly reduced these Ni-MAICs (to around 1×10(-6) molL(-1) at sensitization, with 25 μg mL(-1) LPS, and 1×10(-12) mol L(-1) at elicitation, with 0·5 μg mL(-1) LPS). The effect of LPS depended on its concentration and the timing of its injection.
CONCLUSIONS: Our findings suggest that: (i) Ni-MAIC is higher at sensitization than at elicitation; (ii) once sensitization is established, Ni allergy can easily be induced by a low concentration of Ni; and (iii) a bacterial milieu or infection may greatly facilitate the establishment and elicitation of Ni allergy.