Experimental sensitization of guinea-pigs to nickel and patch testing with metal samples.

Two groups each of 30 guinea-pigs were painted on 5 days/wk for 4 wk with 1% nickel sulphate in lanolin. The dose was applied to the shaved dorsal skin, which was prepared daily before treatment with sodium lauryl sulphate and injected intradermally each week during this period with 0.1 ml 1% potassium alum in distilled water, close to the site of NiSO4 application. Of the two groups of guinea-pigs submitted to this epicutaneous procedure, 63 and 80% developed skin allergy in response to challenge with 2% NiSO4 after a rest period of 2 wk, whereas no sensitization response was elicited by 1% NiSO4 in the guinea-pig maximization test. When two further groups were sensitized by the epicutaneous procedure, the first group, with a sensitization rate of 52% at the first challenge, showed no decline in response with five successive monthly challenges. Addition of NiCl2 to the drinking-water of the second group did not increase the sensitization rate induced by the monthly rechallenges with NiSO4. In guinea-pigs allergic to nickel, plating of Ni-coated brass discs with chromium as a special surface treatment prevented the occurrence of the contact allergy elicited by brass discs coated with Ni alone, whereas plating with gold/copper/cadmium did not.