Low Levels of Endotoxin Enhance Allergen-Stimulated Proliferation and Reduce the Threshold for Activation in Human Peripheral Blood Cells

Abstract

Background: Endotoxins, comprised of bacterial cell wall lipopolysaccharides (LPS), have been reported to have both protective and exacerbating effects on the development and maintenance of allergic disease in humans and on markers of allergic inflammation in animal models of allergy. In this study, we investigated the effect of low concentrations of LPS on human peripheral blood mononuclear cells (PBMC) stimulated with the major cat allergen Fel d 1. Methods: Extensive purification of recombinant (r) Fel d 1 yielded essentially endotoxin-free rFel d 1 (0.2 ng LPS /mg protein). PBMCs prepared from 15 subjects having IgE to cat (>0.7 kU_A/l) and 8 subjects IgE negative to cat were stimulated with 2, 10 or 25 µg/ml of rFel d 1 in the presence or absence of 50 pg/ml LPS. Proliferation was measured after 7 days of culture and supernatants were analyzed for IFNγ, IL-5 and IL-10. Results: LPS (50 pg/ml) increased rFel d 1-stimulated proliferation of PBMCs both from subjects IgE-positive and subjects negative to cat allergens. PBMCs from 13 of the subjects did not proliferate in response to stimulation with 2 and 10 µg/ml rFel d 1 alone but did so in the presence of LPS. Moreover, LPS increased the levels of rFel d 1-stimulated IFNγ in cultures from cat-negative subjects, IL-5 from cat-positive subjects and IL-10 from both groups. Conclusion: Very low doses of LPS enhance proliferation and decrease the apparent threshold level for cell activation, prompting careful evaluation of allergen stimulated T cell activation in vitro.