Pollen grains induce a rapid and biphasic eczematous immune response in atopic eczema patients

Introduction: Eczematous reactions to type I allergy-inducing
antigens are documented in a subgroup of patients with atopic
eczema. Yet, the underlying immunological mechanisms are not well
understood. Material and Methods: To delineate the effect of native
pollen grains on human skin of healthy and atopic individuals we
performed patch tests (atopy patch test with native pollen grains,
PPT). Nickel patch tests (NPT) served as an established model of
contact dermatitis. Skin site biopsies were taken 6 - 96 h after
allergen application and investigated immunohistochemically.
Results: Histology of positive patch tests showed an influx of
mononuclear cells (predominantly CD4+, CD25+, CD45RO+). This influx
was detected earlier in the PPT reaction than in the immune
response to nickel. A biphasic cytokine response could be detected
in the PPT: IL-5 dominated in the early, IFN-gamma in the late
phase. The NPT was continuously dominated by IFN-gamma. Dendritic
cell subpopulations imitated the earlier kinetics of the
mononuclear infiltrate. Discussion: Thus, pollen grains induce
eczematous reactions in susceptible individuals. This reaction
appears clinically and immunohistochemically similar to the contact
hypersensitivity reaction to nickel but follows a faster kinetic
and a biphasic course: Th2 and IgE in the early (24 h) and Th1
predominance in the late (96 h) phase. Copyright (c) 2007 S. Karger
AG, Basel.