The pattern of human late-phase skin reactions to extracts of aeroallergens.

The kinetics and dose response of cutaneous late phase reactions (LPR) (defined as greater than 5 mm induration 6 hours after intradermal challenge with allergen) were studied in 20 randomly selected subjects with atopic rhinitis. When subjects were challenged intradermally with 0.2 biologic unit (BU) of Dermatophagoides pteronyssinus or grass pollen, wheal-and-flare reactions were elicited without subsequent LPRs. With 30 BU, all subjects developed LPRs, whereas 1 and 10 BU provoked LPRs in 28% and 64%, respectively. No biphasic responses were detected. At all concentrations which progressed to form an LPR, a palpable skin reaction was continuously present and either remained constant or increased steadily in magnitude during 6 hours. Skin reactions of similar diameter provoked by histamine resolved fully within 2 hours. Thus, we confirm that the development of a macroscopic cutaneous LPR requires a higher concentration of allergen than the wheal-and-flare reaction. Together with our other findings, these results suggest that all untreated atopic individuals are capable of mounting an LPR if they are challenged with sufficient allergen. In contrast to the asthmatic response to inhaled allergen, the cutaneous wheal and LPR are not biphasic.