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

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 (alpha-BtE IgE) were divided into two groups, according to the presence or absence of skin reactivity to B. tropicalis extract (BtE). The following parameters were investigated: total IgE levels; alpha-BtE IgE levels; an arbitrary alpha-BtE IgE/total IgE ratio; the proportion of carbohydrate-reactive alpha-BtE IgE; the proportion of alpha-BtE IgE that reacted with Ascaris lumbricoides extract (AlE); the production of IL-10 by BtE-and AlE-stimulated peripheral blood cells (PBMC). Results: Total IgE levels were similar in the two groups, but alpha-BtE IgE was significantly higher in the SPT-positive group (SPT+). A large overlap of alpha-BtE 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 alpha-BtE IgE that reacted with carbohydrate and in the production of IL-10 by BtE- and AlE-stimulated PBMC. Both groups had part of alpha-BtE IgE activity absorbed out by AlE, indicating the existence of cross-reactive IgE antibodies. However, the alpha-BtE IgE from the SPT-negative individuals (SPT-) was more absorbed with AlE than the alpha-BtE IgE from the SPT+ individuals. This finding may be ascribed to avidity differences of the alpha-BtE IgE that is present in the two groups of individuals, and could occur if at least part of the alpha-BtE 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 alpha-BtE 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.