MALT1 Controls Attenuated Rabies Virus by Inducing Early Inflammation and T Cell Activation in the Brain

Abstract

MALT1 is involved in the activation of immune responses, as well as in the proliferation and survival of certain cancer cells. MALT1 acts as a scaffold protein for NF-κB signaling and a cysteine protease that cleaves substrates, further promoting the expression of immunoregulatory genes. Deregulated MALT1 activity has been associated with autoimmunity and cancer, implicating MALT1 as a new therapeutic target. Although MALT1 deficiency has been shown to protect against experimental autoimmune encephalomyelitis, nothing is known about the impact of MALT1 on virus infection in the central nervous system. Here, we studied infection with an attenuated rabies virus, Evelyn-Rotnycki-Abelseth (ERA) virus, and observed increased susceptibility with ERA virus in MALT1−/− mice. Indeed, after intranasal infection with ERA virus, wild-type mice developed mild transient clinical signs with recovery at 35 days postinoculation (dpi). Interestingly, MALT1−/− mice developed severe disease requiring euthanasia at around 17 dpi. A decreased induction of inflammatory gene expression and cell infiltration and activation was observed in MALT1−/− mice at 10 dpi compared to MALT1+/+ infected mice. At 17 dpi, however, the level of inflammatory cell activation was comparable to that observed in MALT1+/+ mice. Moreover, MALT1−/− mice failed to produce virus-neutralizing antibodies. Similar results were obtained with specific inactivation of MALT1 in T cells. Finally, treatment of wild-type mice with mepazine, a MALT1 protease inhibitor, also led to mortality upon ERA virus infection. These data emphasize the importance of early inflammation and activation of T cells through MALT1 for controlling the virulence of an attenuated rabies virus in the brain.IMPORTANCE Rabies virus is a neurotropic virus which can infect any mammal. Annually, 59,000 people die from rabies. Effective therapy is lacking and hampered by gaps in the understanding of virus pathogenicity. MALT1 is an intracellular protein involved in innate and adaptive immunity and is an interesting therapeutic target because MALT1-deregulated activity has been associated with autoimmunity and cancers. The role of MALT1 in viral infection is, however, largely unknown. Here, we study the impact of MALT1 on virus infection in the brain, using the attenuated ERA rabies virus in different models of MALT1-deficient mice. We reveal the importance of MALT1-mediated inflammation and T cell activation to control ERA virus, providing new insights in the biology of MALT1 and rabies virus infection.

Inhibition of MALT1 Decreases Neuroinflammation and Pathogenicity of Virulent Rabies Virus in Mice

“…The fact that MALT1 inhibition only slows down rabiesinduced disease progression and cannot prevent lethality may jeopardize such an approach, but extended survival upon initial treatment with MALT1 inhibitors may allow more time for postexposure prophylaxis or other treatments to be effective in acute encephalitis caused by highly virulent rabies viruses. The here-described protective effect of MALT1 inhibition in mice infected with the virulent rabies virus strain CVS-11 is in sharp contrast to the sensitizing effect of MALT1 inhibition that we previously reported in mice infected with an attenuated vaccine rabies virus strain (ERA), which was shown to result from decreased MALT1-mediated T cell activation in the early phase of infection (54). Experimental work with attenuated rabies viruses can give insights on how rabies virus can be controlled and cleared from the brain by the immune system, whereas the use of virulent rabies viruses allows to study the mechanisms of acute and lethal rabies disease.…”

“…In contrast, T cells are much more important in controlling infections caused by attenuated viruses, in which T cells remain intact and infected neurons can be eliminated (52,53). This is also supported by our recent finding that MALT1 deficiency in T cells, leading to decreased T cell activation, strongly sensitizes mice to infection with the attenuated rabies virus strain ERA (54).…”

“…Mice were backcrossed for more than 10 generations into the C57BL/6 background and were intercrossed to generate Malt1 ϩ/ϩ , Malt1 ϩ/Ϫ , and Malt1 Ϫ/Ϫ offspring. Cell type-or lineage-specific Malt1-deficient mice were obtained as described previously (54), and NKp46-iCre line mice (75) were kindly given by Eric Vivier. MALT1 PD mice lacking only the catalytic activity of MALT1 were generated by crossing Malt1 Ϫ/Ϫ and Malt1 PD/ϩ mice (provided by M. Baens).…”

“…A score ranging from 0 (no disease) to 9 (severe brain disease) was attributed to each mouse. Disease signs were scored as described previously (54). Once the mice reached a minimum score of 6 or at different time points following virus inoculation (4 dpi is the incubation phase, and 8 dpi is the end stage of disease), they were euthanized with an overdose of ketamine (100 mg/kg of body weight; Ceva, Brussels, Belgium) and xylazine (9.9 mg/kg; Rompun 2%; Bayer Healthcare, Kiel, Germany) given intraperitoneally (i.p.)…”

Defining the relevant combinatorial space of the PKC/CARD-CC signal transduction nodes

“…The CBM complex signaling is a nice illustration of the double edged role of immune signaling components and the importance for their tight regulation [5]. For example, MALT1 in T cells is critical for immunity to an avirulent strain of Rabies virus [40], but at the same time is T cell-expressed MALT1 also contributing to mortality after infection by a virulent strain of Rabies virus due to excessive inflammation [41]. Disrupted MALT1 protease activity specifically in T cells is also leading to the development of spontaneous autoimmune disease [42].…”