COMPARATIVE STUDY OF 3H-THYMIDINE LABELLING OF THE DERMAL INFILTRATE OF SKIN ALLERGIC AND IRRITANT PATCH TEST REACTIONS IN MAN

Summary.— The 3H-Thymidine (3HT) nuclear labelling index of “round” cells of the dermal infiltrate in allergic and irritant patch test reactions in man has been compared. The skin of 15 positive allergic patch test reactions (to different allergens) and of 15 positive irritant reactions (5 to croton oil, 5 to potassium hydroxide and 5 to white spirit) was biopsied 48 hours after the application of the chemical. Thin slices of each specimen were incubated for 60 min in the presence of 3HT. then fixed and prepared for light microscopy radioautography. Two thousand “round” cells of the infiltrate were counted in each specimen. The mean values of the 3HT labelling indices (±S.E.) were 2·91±0·18%, in the allergic group and 0·58 ± 0·06% in the irritant group. The difference between the 2 means was highly significant (P 0.05). All the labelled cells were mononucleated. This method could be useful to differentiate clinically dubious allergic and irritant reactions.