Comparison of methods for the macroscopic assessment of epicutaneous allergic contact reactions in guinea pigs

Abstract

Guinea pigs (40) were sensitized with a 50% solution of 2,4-dinitro-1-chlorobenzene (DNCB) and challenged 14 days later with DNCB 0.05%. Four parameters were determined to evaluate the challenge reaction after 24, 48, 72 and 96 h: intensity of erythema, reaction area (product of the largest diameters of the reaction in vertical alignment), increase in skinfold thickness and reaction volume (product of the reaction area and the increase in skinfold thickness). The test reactions were read blind by 2 independent observers, yielding small but significant differences in all methods except determination of the reaction area. Further statistical analysis revealed a linear correlation between the intensity of erythema and the other 3 parameters determined, as well as between the reaction area and the reaction volume. In contrast, the increase in skinfold thickness did not correlate linearly either with the reaction area or the reaction volume. When the results of the 24- and 48-h readings were compared, the characteristic crescendo reaction of contact allergy was demonstrable by all methods except the determination of the reaction area. After the 48-h reading, a continuous decrease of reactions was found with all methods. The determination of the reaction area and consequently of the reaction volume evidently are not suitable for exact measurement of epicutaneous allergic contact reactions in guinea pigs. The most precise results will be obtained by measuring the increase in skinfold thickness, whereas the determination of the intensity of erythema, which is easier to perform, may be sufficient for many purposes. Significant inter-individual variation of reading results obtained by different investigators is a critical factor in patch test studies in guinea pigs.