Interleukin (IL-) 4 plays critical roles in immune responses. In particular, the regulated differentiation of type 1 (IFN-gamma) and type 2 (IL-4, IL-5) cytokine production by T cells is controlled by IL-4 and can determine susceptibility to allergic, infectious and autoimmune diseases. Our long-term goal is to understand the molecular mechanisms of IL-4 signal transduction and regulation of gene transcription in lymphoid cells. The differentiation of effector T cell function, and the establishment and maintenance of an antigen-experienced/memory compartment committed to the Th2 cytokine program, are particularly important effects of IL-4. A key objective is to dissect the role of signaling motifs in the IL-4R alpha (IL- 4Ralpha) chain in these processes. However, endogenous IL-4 receptors, and the need to use normal T cells for experiments on Th2 development and memory, have represented technical obstacles. To bypass these obstacles, we created a transgenic mouse model in which expression of a chimeric cytokine receptor was targeted to the T lymphoid lineage. This chimeric cytokine receptor transgene encodes a translational fusion of the IL-2 receptor beta chain ectodomain with the cytoplasmic tail of IL-R4alpha. The chimeric receptor greatly potentiated Th2 development in vitro, and type 2 help was selectively enhanced in vivo. A first goal of the proposed research is to determine the effects of mutations in the IL-4Ralpha tail on Th2 development. A major hypothesis is that the Stat6 signaling pathway collaborates with proliferative and anti-apoptotic signaling pathways in regulating the effect of IL-4 on Th2 development and IL-4 production.
In Specific Aim 1, we will dissect the contributions to Th2 development of motifs in IL-4Ralpha that are known to activate signal transduction pathways. The primary strategy will be to introduce cytokine receptors into activated primary T cells using retroviral transduction, and to compare Th2 development of cells expressing wild-type and mutant IL-4Ralpha sequences.
In Specific Aim 2, we will test the hypothesis that the effect of the chimeric cytokine receptor on memory-phenotype cells spontaneously evolving in vivo differs from its effect on activated effector cells and the antigen experienced/memory-phenotype cells that result after immunization. Programming of memory cells may exert a powerful influence on disease susceptibility. However, very little is known about mechanisms regulating the establishment or maintenance of commitment to programs of effector cytokine production during evolution of memory-phenotype cells. Taken together, the experiments of these Specific Aims will provide new insights into the regulation of the effector and memory-phenotype Th2 subsets.
