A study on the immunological basis of the dissociation between type I-hypersensitivity skin reactions to Blomia tropicalis antigens and serum anti-B. tropicalis IgE antibodies

Abstract

Abstract Background Two conditions are used as markers of atopy: the presence of circulating anti-allergen IgE antibodies and the presence of positive skin prick test (SPT) reactions to allergenic extracts. The correlation between these conditions is not absolute. This study aimed at investigating immunological parameters that may mediate this lack of correlation. Individuals whose sera contained anti-B. tropicalis extract IgE antibodies (α-Bt E IgE) were divided into two groups, according to the presence or absence of skin reactivity to B. tropicalis extract (Bt E). The following parameters were investigated: total IgE levels; α-Bt E IgE levels; an arbitrary α-Bt E IgE/total IgE ratio; the proportion of carbohydrate-reactive α-Bt E IgE; the proportion of α-Bt E IgE that reacted with Ascaris lumbricoides extract (Al E); the production of IL-10 by Bt E- and Al E-stimulated peripheral blood cells (PBMC). Results Total IgE levels were similar in the two groups, but α-Bt E IgE was significantly higher in the SPT-positive group (SPT+). A large overlap of α-Bt E IgE levels was found in individuals of both groups, indicating that these levels alone cannot account for the differences in SPT outcome. Individuals of the two groups did not differ, statistically, in the proportion of α-Bt E IgE that reacted with carbohydrate and in the production of IL-10 by Bt E- and Al E-stimulated PBMC. Both groups had part of α-Bt E IgE activity absorbed out by Al E, indicating the existence of cross-reactive IgE antibodies. However, the α-Bt E IgE from the SPT-negative individuals (SPT-) was more absorbed with AlE than the α-Bt E IgE from the SPT+ individuals. This finding may be ascribed to avidity differences of the α-Bt E IgE that is present in the two groups of individuals, and could occur if at least part of the α-Bt E IgE from the SPT- individuals were elicited by A. lumbricoides infection. Conclusion The present results suggest that a low ratio of specific IgE to total IgE levels (in a minority of individuals), and differences in α-Bt E IgE avidities (which would have high affinities for A. lumbricoides antigens in SPT- than in SPT+ individuals) may play a role in the down-modulation of type-I hypersensitivity reaction against aeroallergens described in helminth-infected individuals.