Impaired response to interferon-alpha/beta and lethal viral disease in human STAT1 deficiency

Immune deficiencies due to defects in cytokine signaling

Severe combined immunodeficiency (SCID) represents a syndrome comprising the most severe forms of inherited immunodeficiencies. Defects in cytokine signaling pathways can result in impaired development of lymphoid cells and/or defective functioning of these cells, and most cases of SCID result from defective signaling through the common cytokine receptor g chain (g(c)) or associated molecules and signaling pathways. Studies of these patients and the analysis of gene-targeted mice provide insight into the underlying signaling defects in inherited immunodeficiencies. The identification of the genetic defects in humans with SCID provides the basis for future therapies for these patients. More subtle deficiencies in cytokine signaling have also been found as causes of other forms of immunodeficiency, and the knowledge learned could lead to novel approaches to antimicrobial therapy.

Dysregulated Sonic hedgehog signaling and medulloblastoma consequent to IFN-alpha-stimulated STAT2-independent production of IFN-gamma in the brain

The type I IFNs (IFN-alpha and IFN-beta), which are crucial in antiviral defense and immune regulation, signal via the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway with activation of STAT1 and STAT2. Here, the function of STAT2 was studied in transgenic mice (termed GIFN/STAT2-/-) with CNS production of IFN-alpha. Surprisingly, GIFN/STAT2-/-, but not GIFN/STAT1-null, transgenic mice, with CNS production of IFN-alpha, died prematurely with medulloblastoma. An immune response also induced in the brain of the GIFN/STAT2-/- mice was associated with IFN-gamma gene expression by CD3+ T cells and the activation of the STAT1, STAT3, STAT4, and STAT5 molecules. Expression of the Sonic hedgehog (Shh) and the downstream transcriptional factor Gli-1 genes, implicated in the pathogenesis of medulloblastoma, was found to be significantly increased and cotranscribed in cerebellar granule neurons of the GIFN/STAT2-/- mice. IFN-gamma, but not IFN-alpha, induced STAT1-dependent expression of the Shh gene in cultured cerebellar granule neurons. Thus, there is an unexpected and extraordinarily adverse biological potency of IFN-alpha in the CNS when the primary signal transduction molecule STAT2 is absent. Moreover, a hitherto unknown role is indicated for the immune system in the pathogenesis of developmental disorders and tumorigenesis of the CNS via dysregulated Shh signaling mediated by IFN-gamma.