INCREASED ALLERGEN-SPECIFIC TH2 RESPONSES IN-VITRO IN ATOPIC SUBJECTSRECEIVING SUBCLINICAL ALLERGEN CHALLENGE

The study aimed to determine whether inhalation of subclinical allerge n doses leads to a shift in the balance between T helper (Th) 1 and Th 2 cells in asthmatic patients. Elevated IgE requires allergen-specific T cells producing cytokines such as interleukin (IL)-4 or IL-13. Inte rferon-gamma (IFN-gamma) produced by Th1 cells counteracts the effects of IL-4. In nature, allergic persons are often exposed to low levels of allergen, leading to hyperreactivity, but not to acute allergic rea ctions. In this study, nine allergic persons inhaled low doses of alle rgen or placebo in a double-blind manner over seven consecutive weekda ys. During the study, the bronchial responsiveness to histamine challe nge increased, but no subject exhibited asthmatic symptoms. Blood was drawn on days 0, 1, 4, and 9, and the number of IL-4-and IFN-gamma-pro ducing cells was measured by enzyme-linked immunospot (ELISPOT) assay after in vitro stimulation with a low-dose phytohemagglutinin (PHA) mi xed with the relevant allergen or with PHA alone. In three of the four subjects receiving allergen, the IL-4/IFN-gamma ratio increased durin g the time of the study. No increase was seen in the placebo Stockholm University group. No increase was seen in serum IgE levels in any of the groups. We stockholm conclude that a shift in the balance between Th1 and Th2 cells can be detected in subjects exposed to subclinical a llergen doses.