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 primary culture have led to widespread reliance on less physiologic approaches to T cell activation. Although there is general agreement of a Th2-like bias, the precise defects in cytokine responsiveness remain controversial. Analysis of cytokine protein production by fresh, unselected cell populations in response to cognate, antigen-driven stimulation remains an important goal. Here, limiting dilution analysis (LDA) was used to evaluate antigen-stimulated cytokine gene expression by fresh 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 clinically non-allergic individuals exhibited virtually equivalent antigen-specific, CD4-dependent cytokine production in response to short-term culture with these common environmental antigens. As anticipated, pronounced increases in Th2-like activity were evident in the circulating 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 rhinitis (Mann-Whitney U-test, P = 0. 00067). This Th2-like bias reflected both a lower frequency of IFN-gamma-producing cells and a markedly increased frequency of IL-4-producing cells in the circulating grass-pollen specific repertoire of atopic donors. The observation that every atopic and normal subject produced IFN-gamma (+/-IL-4) following antigen re-stimulation argues that the decision as to whether allergy or (clinical) tolerance results, hinges not on a genetically determined capacity of whether allergen-reactive T cells can be stimulated in any given individual by chronic exposure to ubiquitous environmental antigens, but on the nature of the cytokine response that comes to dominate that individual's response.