ALLERGEN-DRIVEN LIMITING DILUTION ANALYSIS OF HUMAN IL-4 AND IFN-GAMMA PRODUCTION IN ALLERGIC RHINITIS AND CLINICALLY TOLERANT INDIVIDUALS

Difficulties in detecting human IL-4 synthesis in antigen-driven prima ry culture have led to widespread reliance on less physiologic approac hes to T cell activation, Although there is general agreement of a T(h )2-like bias, the precise defects in cytokine responsiveness remain co ntroversial, Analysis of cytokine protein production by fresh, unselec ted cell populations in response to cognate, antigen-driven stimulatio n remains an important goal, Here, limiting dilution analysis (LDA) wa s used to evaluate antigen-stimulated cytokine gene expression by fres h peripheral blood mononuclear cells (PBMC), PBMC from 19 grass pollen sensitive, allergic rhinitis subjects and normal, non-atopic controls were evaluated 1 month after natural reimmunization (the peak of the local grass pollen season), Surprisingly, highly atopic subjects and c linically non-allergic individuals exhibited virtually equivalent anti gen-specific, CD4-dependent cytokine production in response to short-t erm culture with these common environmental antigens, As anticipated, pronounced increases in T(h)2-like activity were evident in the circul ating immune repertoire of grass pollen sensitive individuals, leading to a median ratio of antigen-stimulated IFN-gamma:IL-4 frequencies of 117:1 among normal subjects versus 4:1 among those with allergic rhin itis (Mann-Whitney U-test, P = 0.00067), This T(h)2-like bias reflecte d both a lower frequency of IFN-gamma-producing cells and a markedly i ncreased frequency of IL-4-producing cells in the circulating grass-po llen specific repertoire of atopic donors, The observation that every atopic and normal subject produced IFN-gamma (+/-IL-4) following antig en re-stimulation argues that the decision as to whether allergy or (c linical) tolerance results, hinges not on a genetically determined cap acity of whether allergen-reactive T cells can be stimulated in any gi ven individual by chronic exposure to ubiquitous environmental antigen s, but on the nature of the cytokine response that comes to dominate t hat individual's response.