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Departments of Medicine and Microbiology/Immunology, University of California San Francisco, San Francisco, California 94143; and the Department of Genetics, Case Western Reserve University School of Medicine, Cleveland, Ohio 44109
The dysregulated expression of interleukin 4 (IL-4) can have deleterious effects on the outcome of infectious and allergic diseases. Despite this, the mechanisms by which naive T cells commit to IL-4 expression during differentiation into mature effector cells remain incompletely defined. As compared to cells from most strains of mice, activated CD4+ T cells from BALB mice show a bias towards IL-4 production and T helper 2 commitment in vitro and in vivo. Here, we show that this bias arises not from an increase in the amount of IL-4 produced per cell, but rather from an increase in the proportion of CD4+ T cells that commit to IL-4 expression. This strain-specific difference in commitment was independent of signals mediated via the IL-4 receptor and hence occurred upstream of potential autoregulatory effects of IL-4. Segregation analysis of the phenotype in an experimental backcross cohort implicated a polymorphic locus on chromosome 16. Consistent with a role in differentiation, expression of the phenotype was CD4+ T cell intrinsic and was evident as early as 16 h after the activation of naive T cells. Probabilistic gene activation is proposed as a T cell–intrinsic mechanism capable of modulating the proportion of naive T cells that commit to IL-4 production.
Key Words: interleukin 4 • T helper 2 • cytokine expression • genetic analysis • BALB/c mice
1 Abbreviations used in this paper: dice, determinant of IL-4 commitment; HPRT, hypoxanthine phosphoribosyltransferase; QTL, quantitative trait locus.
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