Effect of endotoxin contamination on the antigenic skin test response

Bacterial lipopolysaccharides (LPS), the major part of endotoxin, are proinflammatory substances present in the natural environment. Lipopolysaccharides enhance allergen-induced histamine release from human basophils of allergic subjects. The aim of this study was to assess the LPS activity on the allergy skin test response. Twenty patients allergic to house dust mite (HDM) underwent skin prick tests with LPS (E coli 026: B6 serotype) at concentrations of 1, 10, 100 micrograms/mL, with HDM extracts at different dilutions, and with solutions of LPS mixed with HDM. Endotoxin alone did not induce any immediate skin response; LPS had a synergistic effect on the HDM skin response both in terms of flare [27.4 +/- 2.8 mm, 26.6 +/- 3.3 mm, 28.1 +/- 2.5 mm versus 20.7 +/- 3.6 mm, respectively in presence of LPS 1 (P less than .02), 10 (P less than .05), 100 (P less than .01) micrograms/mL] and wheal response [6.4 +/- 1.0 mm, in presence of LPS 100 micrograms/mL versus 4.9 +/- 1.1 mm in absence of LPS (P less than .05)]. On the other hand, a possible LPS synergistic action on the histamine skin response was evaluated in ten normal subjects but the results were not significant. These findings show that LPS increases the allergy skin response probably due to a mechanism including a potentiation of the IgE receptor activation rather than an increase of the skin response to the release mediators.