ISG15/USP18/STAT2 is a molecular hub regulating IFN I-mediated control of Dengue and Zika virus replication

The establishment of a virus infection is the result of the pathogen's ability to replicate in a hostile environment generated by the host's immune system. Here, we found that ISG15 restricts Dengue and Zika viruses' replication through the stabilization of its binding partner USP18. ISG15 expression was necessary to control DV replication driven by both autocrine and paracrine type one interferon (IFN-I) signaling. Moreover, USP18 competes with NS5-mediated STAT2 degradation, a major mechanism for establishment of flavivirus infection. Strikingly, reconstitution of USP18 in ISG15-deficient cells was sufficient to restore the STAT2's stability and restrict virus growth, suggesting that the IFNAR-mediated ISG15 activity is also antiviral. Our results add a novel layer of complexity in the virus/host interaction interface and suggest that NS5 has a narrow window of opportunity to degrade STAT2, therefore suppressing host's IFN-I mediated response and promoting virus replication.

[Testing for antibodies to tick-borne encephalitis virus using blood dried on filter paper]

Possibility to use blood dried on filter paper for serological testing on antibodies to tick-borne encephalitis (TBE). Sensitivity and specificity of specific IgM detection in dry stains of blood by lanthanide fluorescence immunoassay was 94.9% (86.9-100%) and 97.5% (94-100%) respectively, compared with results obtained in tests of sera. Agreement in positive and negative results of tests for IgM against TBE in 562 serum samples and dry blood stains was 95.3%. During analysis of both types of biomaterial high degree of correlation was observed between intensity of fluorescence when testing for both IgM (r=0.86700; p=0.05; n=562), and IgG (r=0.83883; p=0.05; n=337) toTBE virus. Use of this mildly invasive technique of blood draw is reasonable during conduction of large-scale population studies for seroepidemiologic monitoring, investigation of disease outbreaks, control of effectiveness of vaccination against TBE, assessing of level of specific immunity in population of endemic regions, control of treatment, and serologic diagnostics of acute TBE in hospitalized patients, in which blood draw is difficult to perform.

[Lanthanide immunofluorescence assay for the serodiagnosis of tick-borne encephalitis]

Lanthanide immunofluorescence assay (LIFA) was used to detect IgM of antibodies to tick-borne encephalitis (TBE) virus in 791 patients who had been fallen ill with acute febrile diseases in the period of seasonal activity of carrier ticks in the endemic region of Russia (the Perm Region) (1786 sera being tested). This assay was equally effective as the commercial enzyme immunoassay test system (EITS) in the early serological diagnosis of TBE, verifying the clinical diagnosis in about 70% of patients just within the first week of disease. At the same time, the sensitivity of LIFA was much (nearly 5 times) higher than that of EITS in revealing antibody IgM in patients with chronic TBE, as well as in those with the acute course of disease, accompanied by the low level and untypical trend of accumulation of antibodies ofthis class.

[Choosing the threshold level in the detecting of antibodies to the causative agents of Ixodes tick-borne borreliosis by lanthanide immonofluorescence assay]

The paper describes the algorithm of choice of the threshold level of fluorescence, which identifies the positive and negative results of lanthanide immunofluorescence assay when IgM and IgG antibodies to the causative agents of Ixodes tick-borne borreliosis are detected in the sera of patients. The diagnostic specificity index of the method in detecting antibodies of both types was 95.3% for the chosen value. According to the time of sampling, the diagnostic sensitivity indices for IgM and IgG antibodies were 10.4 to 40.9% and 3.3 to 18.2%, respectively.