The ability of a series of mercaptans, i.e. 2-mercaptoethanol, 1-cysteine, C-acetyl-cysteine, N-acetyl-cysteine, β-β-dimethyl-cysteine and cysteamine, to inactivate skin sensitizing antibodies in the serum of ragweed allergic individuals was studied. Following in vitro reductions and alkylations, 2-mercaptoethanol was shown to be the only mercaptan capable of destroying completely reaginic activity at 0.08–0.1 M. The other mercaptans, under similar conditions, were able to reduce only partially the skin-sensitizing activity. Some reaginic activity was restored if reoxidation of the reduced allergic serum was not prevented. However, it was shown that mixtures of allergic serum and mercaptan, when injected into monkey skin, did not regain skin sensitizing activity. Moreover, pre-treatment of monkey skin with mercaptan did not detectably affect the ability of the skin to fix human reagins.
C-acetyl-cysteine was used for testing its efficacy of inactivating reagins in vivo in monkeys; it was demonstrated that the PCA titres of a human allergic serum were thus decreased by a factor of 8 following administration of the mercaptan to monkeys.