Interferon-induced Parkinsonism in a patient with chronic hepatitis C

Interferons: A molecular switch between damage and repair in ageing and Alzheimer's disease

Alzheimer's disease was first described over 100 years ago, yet it remains incurable and affects 44 million people worldwide. Traditionally, research has largely focused on the amyloid cascade hypothesis, but interest in the importance of inflammation in the progression of the disease has recently been increasing. Interferons, a large family of cytokines that trigger the immune system, are believed to play a crucial role in the pathology of Alzheimer's disease. This review focuses on how interferons affect the brain during ageing and whether they could be candidate therapeutic targets for the treatment of Alzheimer's disease.

Evidence for association between hepatitis C virus and Parkinson's disease

Parkinson's disease (PD) is a globally prevalent neurodegenerative disorder, characterized by progressive neuronal loss in the substantia nigra and formation of Lewy bodies. These pathological characteristics are clinically translated into motor symptoms, such as bradykinesia, rigidity, resting tremors, and postural instability. Emerging data from epidemiological studies suggest a possible association between PD and hepatitis C virus (HCV) infection, which affects up to 71 million individuals worldwide. Preclinical studies have shown that HCV can penetrate and replicate within the brain macrophages and microglial cells, increasing their production of pro-inflammatory cytokines that can directly cause neuronal toxicity. Other studies reported that interferon, previously used to treat HCV infection, can increase the risk of PD through inhibition of the nigrostriatal dopaminergic transmission or induction of neuroinflammation. In this article, we provide a comprehensive review on the possible association between HCV infection and PD and highlight recommendations for further research and practice in this regard.

Type-1 interferons contribute to the neuroinflammatory response and disease progression of the MPTP mouse model of Parkinson's disease

Type-1 interferons (IFNs) are pleiotropic cytokines with a critical role in the initiation and regulation of the pro-inflammatory response. However, the contribution of the type-1 IFNs to CNS disorders, specifically chronic neuropathologies such as Parkinson's disease is still unknown. Here, we report increased type-1 IFN signaling in both post mortem human Parkinson's disease samples and in the 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) mouse model. In response to MPTP, mice lacking the type-1 IFN receptor (IFNAR1(-/-) ) displayed decreased type-1 IFN signaling, an attenuated pro-inflammatory response and reduced loss of dopaminergic neurons. The neuroprotective potential of targeting the type-1 IFN pathway was confirmed by reduced neuroinflammation and DA cell death in mice treated with a blocking monoclonal IFNAR1 (MAR-1) antibody. The MPTP/MAR-1 treated mice also displayed increased striatal dopamine levels and improved behavioural outcomes compared to their MPTP/IgG controls. These data, implicate for the first time, a deleterious role for the type-1 IFNs as key modulators of the early neuroinflammatory response and therefore the neuronal cell death in Parkinson's disease. GLIA 2016;64:1590-1604.

Neuronal MHC-I expression and its implications in synaptic function, axonal regeneration and Parkinson's and other brain diseases

Neuronal expression of major histocompatibility complex I (MHC-I) has been implicated in developmental synaptic plasticity and axonal regeneration in the central nervous system (CNS), but recent findings demonstrate that constitutive neuronal MHC-I can also be involved in neurodegenerative diseases by playing a neuroinflammtory role. Recent reports demonstrate its expression in vitro and in human postmortem samples and support a role in neurodegeneration involving proinflammatory cytokines, activated microglia and increased cytosolic oxidative stress. Major histocompatibility complex I may be important for both normal development and pathogenesis of some CNS diseases including Parkinson's.

MHC-I expression renders catecholaminergic neurons susceptible to T-cell-mediated degeneration

Subsets of rodent neurons are reported to express major histocompatibilty complex class I (MHC-I), but such expression has not been reported in normal adult human neurons. Here we provide evidence from immunolabel, RNA expression, and mass spectrometry analysis of postmortem samples that human catecholaminergic substantia nigra and locus coeruleus neurons express MHC-I, and that this molecule is inducible in human stem cell derived dopamine (DA) neurons. Catecholamine murine cultured neurons are more responsive to induction of MHC-I by gamma-interferon than other neuronal populations. Neuronal MHC-I is also induced by factors released from microglia activated by neuromelanin or alpha-synuclein, or high cytosolic DA and/or oxidative stress. DA neurons internalize foreign ovalbumin and display antigen derived from this protein by MHC-I, which triggers DA neuronal death in the presence of appropriate cytotoxic T-cells. Thus, neuronal MHC-I can trigger antigenic response, and catecholamine neurons may be particularly susceptible to T cell-mediated cytotoxic attack.

Safety, Tolerability, and Immunogenicity of Interferons

Interferons (IFNs) are class II cytokines that are key components of the innate immune response to virus infection. Three IFN sub-families, type I, II, and III IFNs have been identified in man, Recombinant analogues of type I IFNs, in particular IFNα2 and IFNβ1, have found wide application for the treatment of chronic viral hepatitis and remitting relapsing multiple sclerosis respectively. Type II IFN, or IFN gamma, is used principally for the treatment of chronic granulomatous disease, while the recently discovered type III IFNs, also known as IFN lambda or IL-28/29, are currently being evaluated for the treatment of chronic viral hepatitis. IFNs are in general well tolerated and the most common adverse events observed with IFNα or IFNβ therapy are “flu-like” symptoms such as fever, headache, chills, and myalgia. Prolonged treatment is associated with more serious adverse events including leucopenia, thrombocytopenia, increased hepatic transaminases, and neuropsychiatric effects. Type I IFNs bind to high-affinity cell surface receptors, composed of two transmembrane polypeptides IFNAR1 and IFNAR2, resulting in activation of the Janus kinases Jak1 and Tyk2, phosphorylation and activation of the latent cytoplasmic signal transducers and activators of transcription (STAT1) and STAT2, formation of a transcription complex together with IRF9, and activation of a specific set of genes that encode the effector molecules responsible for mediating the biological activities of type I IFNs. Systemic administration of type I IFN results in activation of IFN receptors present on essentially all types of nucleated cells, including neurons and hematopoietic stem cells, in addition to target cells. This may well explain the wide spectrum of IFN associated toxicities. Recent reports suggest that certain polymorphisms in type I IFN signaling molecules are associated with IFN-induced neutropenia and thrombocytopenia in patients with chronic hepatitis C. IFNγ binds to a cell-surface receptor composed of two transmembrane polypeptides IFGR1 and IFGR2 resulting in activation of the Janus kinases Jak1 and Jak2, phosphorylation of STAT1, formation of STAT1 homodimers, and activation of a specific set of genes that encode the effector molecules responsible for mediating its biological activity. In common with type I IFNs, IFNγ receptors are ubiquitous and a number of the genes activated by IFNγ are also activated by type I IFNs that may well account for a spectrum of toxicities similar to that associated with type I IFNs including “flu-like” symptoms, neutropenia, thrombocytopenia, and increased hepatic transaminases. Although type III IFNs share the major components of the signal transduction pathway and activate a similar set of IFN-stimulated genes (ISGs) as type I IFNs, distribution of the IFNλ receptor is restricted to certain cell types suggesting that IFNλ therapy may be associated with a reduced spectrum of toxicities relative to type I or type II IFNs. Repeated administration of recombinant IFNs can cause in a break in immune tolerance to self-antigens in some patients resulting in the production of neutralizing antibodies (NABs) to the recombinant protein homologue. Appearance of NABs is associated with reduced pharmacokinetics, pharmacodynamics, and a reduced clinical response. The lack of cross-neutralization of IFNβ by anti-IFNα NABs and vice versa, undoubtedly accounts for the apparent lack of toxicity associated with the presence of anti-IFN NABs with the exception of relatively mild infusion/injection reactions.