Prophylaxis and therapy of virulent encephalomyocarditis virus infection in mice by monoclonal antibodies. Brief report

c-FLIP-Short reduces type I interferon production and increases viremia with coxsackievirus B3

Cellular FLIP (c-FLIP) is an enzymatically inactive paralogue of caspase-8 and as such can block death receptor-induced apoptosis. However, independent of death receptors, c-FLIP-Long (c-FLIP_L) can heterodimerize with and activate caspase-8. This is critical for promoting the growth and survival of T lymphocytes as well as the regulation of the RIG-I helicase pathway for type I interferon production in response to viral infections. Truncated forms of FLIP also exist in mammalian cells (c-FLIP_S) and certain viruses (v-FLIP), which lack the C-terminal domain that activates caspase-8. Thus, the ratio of c-FLIP_L to these short forms of FLIP may greatly influence the outcome of an immune response. We examined this model in mice transgenically expressing c-FLIP_S in T cells during infection with Coxsackievirus B3 (CVB3). In contrast to our earlier findings of reduced myocarditis and mortality with CVB3 infection of c-FLIP_L-transgenic mice, c-FLIP_S-transgenic mice were highly sensitive to CVB3 infection as manifested by increased cardiac virus titers, myocarditis score, and mortality compared to wild-type C57BL/6 mice. This observation was paralleled by a reduction in serum levels of IL-10 and IFN-α in CVB3-infected c-FLIP_S mice. In vitro infection of c-FLIP_S T cells with CVB3 confirmed these results. Furthermore, molecular studies revealed that following infection of cells with CVB3, c-FLIP_L associates with mitochondrial antiviral signaling protein (MAVS), increases caspase-8 activity and type I IFN production, and reduces viral replication, whereas c-FLIP_S promotes the opposite phenotype.

Influence of epitope polarity and adjuvants on the immunogenicity and efficacy of a synthetic peptide vaccine against Semliki Forest virus

The antibody response to a previously defined B-cell epitope of Semliki Forest virus (SFV) was investigated in male BALB/c (H-2d) mice. The B-cell epitope, located at amino acid positions 240 to 255 of the E2 protein, was linked to an H-2d-restricted T-helper cell epitope of SFV located at positions 137 to 151 of the E2 protein. Colinearly synthesized peptides, of either T-B or B-T polarity, mixed with different adjuvants (the nonionic block copolymer L 180.5, a water-oil-water [W/O/W] emulsion of L 180.5, Montanide, and Q VAC) were used for immunization. Generally, after one booster immunization, high serum antibody titers were measured against either peptide. With Q VAC and W/O/W L 180.5 as adjuvants, the titers of SFV-reactive (nonneutralizing) antibodies were consistently much higher after immunization with the T-B peptide than with the B-T peptide, which was reflected in a higher vaccine efficacy. With these two adjuvants, the survival ratio in T-B peptide-immunized mice was 82%, compared with 8% in B-T peptide-immunized mice. Intermediate results were obtained with the adjuvant Montanide. L 180.5 alone was ineffective in this study. All immunoglobulin G (IgG) isotypes were induced with either adjuvant, but Q VAC was clearly the most effective in inducing IgG2a and IgG2b isotypes with the T-B peptide as the antigen. Subsequently, monoclonal antibodies (MAbs) of IgM, IgG1, IgG2a, IgG2b, and IgG3 subclasses were prepared against the B-cell epitope. These nonneutralizing but SFV-reactive MAbs protected 40 to 80% of mice against a lethal challenge with SFV. Control mice all died. The availability of those antipeptide MAbs allowed competition binding assays with a previously characterized panel of E2-specific MAbs. Binding of enzyme-labeled antipeptide MAbs was very effectively inhibited by two strongly SFV-neutralizing mutually competitive MAbs, suggesting that the linear B-cell epitope (amino acids 240 to 255) is associated with a major neutralization site of SFV.

Detection of a shared idiotope on two encephalomyocarditis virus neutralizing monoclonal antibodies by neutralization inhibition enzyme immunoassay

Idiotypic cross-reactivity between encephalomyocarditis virus (EMCV) neutralizing monoclonal antibodies UM 21.1 (IgG2b) and UM 21.3 (IgG2a) was detected by neutralization inhibition enzyme immunoassay using polyclonal and monoclonal anti-idiotypic antibodies. One strongly cross-reactive anti-idiotypic monoclonal antibody, designated 21.1A5 (IgG2b), might recognize a recurrent idiotope on EMCV neutralizing antibodies but it did not induce EMCV neutralizing anti-anti-idiotypic antibodies in homologous BALB/c mice.

A vaccine against Semliki Forest virus consisting of a monoclonal anti-idiotypic antibody cross-linked to a protein which contains virus-specific T-helper cell epitopes

A recombinantly expressed protein, consisting of cro-beta-galactosidase at the N-terminus and amino acid residues 115 to 151 of the E2 membrane of Semliki Forest virus (SFV) at the C-terminus containing two T-helper cell epitopes of SFV, was cross-linked with glutaraldehyde to a noninternal image monoclonal anti-idiotypic antibody (ab2 alpha MAb) able to induce SFV-neutralizing anti-anti-idiotypic (ab3) antibodies in BALB/c mice. This vaccine, which might potentially induce SFV-specific T-helper cell memory, established in BALB/c mice a state of protective immunity against virulent SFV within 10 days of immunization. A steady rise in serum neutralization titre occurred from day 7 to day 28 after primary anti-idiotypic immunization, levelling off thereafter. In primarily immunized mice significant rises of serum neutralization titres, which could be indicative for an operational T-helper cell memory, were not observed after challenge on day 35 with virulent SFV. The results suggest that SFV is neutralized by ab3 antibodies shortly after challenge, preventing, thereby, virus multiplication to levels sufficient to provoke a measurable booster response.

Efficient induction of Semliki Forest virus and mumps virus neutralizing anti-anti-idiotypic antibodies using Quil A as adjuvant

Rabbit anti-idiotypic sera were prepared against Semliki Forest virus (SFV) neutralizing monoclonal antibody (MAb) UM 1.13 and mumps virus neutralizing MAb UM 10B. From these sera anti-idiotypic antibodies were purified by ammonium sulphate precipitation and subsequent affinity column chromatography. Anti-iso- and anti-allotypic antibodies were removed by binding to normal mouse serum immunoglobulins coupled to CNBr activated Sepharose. Peak protein fractions eluted from columns loaded with homologous MAb were used for anti-anti-idiotypic immunization of BALB/c mice to raise virus neutralizing anti-anti-idiotypic antibodies. Two intracutaneous immunizations, five weeks apart, with affinity purified rabbit polyclonal anti-idiotypic antibody (40 micrograms protein per animal) coupled to keyhole limpet hemocyanin and mixed with the adjuvant Quil A (50 microliters per animal) were sufficient to evoke neutralizing antibodies against either virus. Moreover the mice who developed SFV neutralizing serum antibodies upon anti-idiotypic immunization all survived an otherwise lethal challenge with virulent SFV.

A protective monoclonal anti-idiotypic vaccine to lethal Semliki Forest virus infection in BALB/c mice

Two monoclonal anti-idiotypic antibodies (ab2 MAbs), designated 1.13A112 (immunoglobulin G type 2a [IgG2a]) and 1.13A321 (IgG1), were prepared against Semliki Forest virus (SFV)-neutralizing ab1 MAb UM 1.13. They were identified in hybridoma supernatant fluid by their capacity to block UM 1.13-mediated neutralization of SFV. Although the neutralization-blocking capacities of the ab2 MAbs did not differ, only 1.13A321 evoked SFV-neutralizing ab3 antibodies upon intracutaneous and subcutaneous immunization of BALB/c mice with 1.13A321 chemically cross-linked to keyhole limpet hemocyanin and combined with the adjuvant Quil A. SFV-neutralizing ab3 antibodies appeared in serum within 10 days after primary immunization, and neutralizing antibody titers could be as high as 1/1,000 at day 35. All mice who had developed SFV-neutralizing antibodies upon anti-idiotypic immunization survived an otherwise lethal challenge with virulent SFV. However, induction of SFV-neutralizing ab3 antibodies by ab2 MAb 1.13A321 proved to be genetically restricted to BALB/c mice; even haplotype-identical (H-2d) DBA/2 mice did not respond, and consequently those animals died after infection with virulent SFV.

Blocking by anti-idiotypic antibodies of monoclonal antibody mediated protection in mice against encephalomyocarditis virus induced diabetes and lethal disease

Monoclonal antibodies (MA) UM 21.1 and UM 21.2 protect mice against encephalomyocarditis virus (D-variant) induced diabetes and lethal disease. MA-mediated protection in vivo as well as neutralization in vitro could be specifically blocked by anti-idiotypic antibodies.

Competition binding assay in cell culture for identification of epitopes on enveloped and naked viruses

Virus infected monolayers, in wells of 96-well plates, could be used as antigen in competition binding assays to identify epitopes on respectively Semliki Forest virus, encephalomyocarditis virus and mumps virus.

Rapid bioassay of human interferon by direct enzyme immunoassay of encephalomyocarditis virus in HEp-2 cell monolayers after a single cycle of infection

Multiplication of encephalomyocarditis virus (EMCV) in human HEp-2 cells, and its suppression by interferon (IFN), was demonstrated by direct enzyme immunoassay (EIA) in cell culture. EMCV was detected in glutaraldehyde fixed HEp-2 cell monolayers, in wells of 96-well plates, with a horse radish peroxidase (HRPO) labelled EMCV specific monoclonal antibody. Multiplication of EMCV (multiplicity of infection: 50) was indicated by a steep rise of absorbance values measured against infected monolayers starting as early as 5 h after infection and reaching relatively high values at 6 and 7 h. The rise in absorbance values did not occur after preincubation of the HEp-2 cells with either Newcastle disease virus-induced IFN, recombinant gamma IFN or recombinant alfa-2a IFN. Absorbance values were inversely dependent on the amount of IFN used. Therefore the EIA was suitable for rapid titration of IFN. The titres of recombinant gamma and alfa-2a IFN determined with EIA proved to be similar to those given by the manufacturers. The described bioassay of human IFN is objective, rapid and easy to perform and suitable for large scale experiments.

Application of immunoassay of encephalomyocarditis virus in cell culture with enzyme-labeled virus-specific monoclonal antibodies for rapid detection of virus, neutralizing antibodies, and interferon

Encephalomyocarditis virus (EMCV)-specific monoclonal antibody UM 21.1 labeled with horseradish peroxidase was used to detect EMCV in L-cell monolayers. This direct enzyme immunoassay of EMCV, performed in wells of 96-well plates, could be applied for various purposes, such as early detection of virus multiplication, determination of 50% tissue culture infective doses, and rapid titration of interferon and EMCV-neutralizing antibodies. Multiplication of EMCV is indicated by a rapid increase of the absorbance values measured against EMCV-infected L cells starting as early as 4.5 h after virus inoculation. The early rise of absorbance (i.e., virus multiplication) is inhibited by interferon, allowing its rapid titration. Preincubation of the virus inoculum with neutralizing antibodies also yielded decreased absorbance values. With the latter enzyme immunoassay for neutralizing antibodies, performed after an infection period of 8 h, antibody titers measured were comparable to those obtained with a conventional plaque reduction test. We assume that similar assays could be developed for other picornaviruses (e.g., polioviruses).

Discrimination of determinant specificity of two encephalomyocarditis virus neutralizing monoclonal antibodies by competition, mixed neutralization and anti-idiotypic antibodies

To investigate the epitope(s) on encephalomyocarditis virus (EMCV) involved in neutralization, two neutralizing monoclonal antibodies (MAs) (MA UM 21.1 and MA UM 21.2) were tested in a competition binding assay (CBA), a mixed neutralization test and an enzyme immunoassay (EIA) with specificity for the detection of idiotypes on MAs. With a CBA in cell culture, using EMCV infected L cell monolayers as binding antigen, strong homologous competition was observed between unlabelled MAs and horse radish peroxidase (HRPO-) labelled MAs but considerable heterologous competition did also occur, especially between the unlabelled MA UM 21.1 and HRPO-labelled MA UM 21.2. In the mixed neutralization test (50% plaque reduction) preincubation with slightly neutralizing or nonneutralizing doses of MA UM 21.2 had no diminishing effect on the neutralizing capacity of MA UM 21.1, the PRT50 value remains in all cases -10log titre of 5.8. Furthermore rabbit polyclonal antibodies against the idiotypes of MAs UM 21.1 and UM 21.2 did not cross react in the EIA. In conclusion both MAs recognize different viral determinants as indicated by the results obtained with a CBA, a mixed neutralization test and an EIA for detection of idiotypes on MAs.