IL-7 Promotes TH1 Development and Serum IL-7 Predicts Clinical Response to Interferon-β in Multiple Sclerosis

The interleukin-7 receptor a chain (IL-7R alpha) gene was identified as a top non-major histocompatibility complex-linked risk locus for multiple sclerosis (MS). Recently, we showed that a T helper 1 (T(H)1)-driven, but not a T(H)17-driven, form of MS exhibited a good clinical response to interferon-beta (IFN-beta) therapy. We now demonstrate that high serum levels of IL-7, particularly when paired with low levels of IL-17F, predict responsiveness to IFN-beta and hence a T(H)1-driven subtype of MS. We also show that although IL-7 signaling is neither necessary nor sufficient for the induction or expansion of T(H)17 cells, IL-7 can greatly enhance both human and mouse T(H)1 cell differentiation. IL-7 alone is sufficient to induce human T(H)1 differentiation in the absence of IL-12 or other cytokines. Furthermore, targeting IL-7/IL-7R alpha is beneficial in experimental autoimmune encephalomyelitis (EAE), a mouse model of MS. Mice treated with IL-7R alpha-blocking antibodies before or after onset of paralysis exhibited reduced clinical signs of EAE, with reduction in peripheral naive and activated T cells, whereas central memory T, regulatory T, B, and natural killer cell populations were largely spared. IL-7R alpha antibody treatment markedly reduced lymphocyte infiltration into the central nervous system in mice with EAE. Thus, a serum profile of high IL-7 may signify a T(H)1-driven form of MS and may predict outcome in MS patients undergoing IFN-beta therapy. Blockade of IL-7 and the IL-7R alpha pathway may have therapeutic potential in MS and other autoimmune diseases.