Delayed-type hypersensitivity against Semliki Forest virus in mice

Inhibition of Semliki Forest virus multiplication in L-cells by combinations of interferon and ribavirin as measured by plaque titration and direct enzyme immunoassay

Inhibition of Semliki Forest virus (SFV) multiplication in L-cell monolayers by combinations of mouse interferon (IFN) and ribavirin was measured by plaque titration and by direct enzyme immunoassay of SFV in L-cells. When critically inhibitory quantities of IFN and ribavirin were combined, an additive inhibitory effect was observed in either assay.

Identification of a DTH-inducing T-cell epitope on the E2 membrane protein of Semliki Forest virus

Mapping of T-cell epitopes on the structural proteins of Semliki Forest virus (SFV) was performed by measuring the ability of cloned SFV protein fragments to induce delayed-type hypersensitivity (DTH). The cloned SFV protein fragments were expressed as hybrid proteins with cro-beta-galactosidase in Escherichia coli from constructed recombinant plasmids. DTH reactions were measured, as footpad swelling, in BALB/c mice after immunization with whole, UV-inactivated SFV and challenge with the hybrid proteins, and vice versa, using the adjuvant dimethyl dioctadecyl ammonium bromide to enhance DTH. Only two of the tested hybrid proteins induced DTH, and these DTH reactions were equally strong. The largest DTH-inducing hybrid protein contained the N-terminal 350 amino acids of E2 and part of E3, the smallest contained only the region from amino acid residues 115 to 151 of the E2 membrane protein without any other SFV protein parts. It was concluded that the segment between amino acid residues 115 and 151 of the E2 membrane protein of SFV was responsible for the observed DTH, and thus, contains a T-cell epitope. Sequence homology with known T-cell epitopes on other proteins makes it likely that the DTH-inducing T-cell epitope is located from amino acid residues 120 to 128 of E2.

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 determination of neutralizing antibodies to Semliki Forest virus in serum by enzyme immunoassay in cell culture with virus-specific monoclonal antibodies

We describe in this study a rapid enzyme immunoassay for the titration of neutralizing antibodies in serum against Semliki Forest virus. For this assay L cells were added to preincubated virus-antiserum mixtures to form monolayers. Six hours after infection by residual, nonneutralized virus, the monolayers were fixed, and the E2 glycoprotein of Semliki Forest virus on the surface of infected cells was quantified with an E2-specific, peroxidase-labeled monoclonal antibody (UM 5.1). The serum antibody titer was defined arbitrarily as the inverse value of that dilution of serum associated with a 25% inhibition of control absorbance values. These titers of both early and later mouse immune sera were similar to those determined in simultaneously performed 50% plaque reduction tests. The results indicate that the enzyme immunoassay (duration, 9 h) is reliable and compares favorably with the conventional plaque reduction test (duration, 25 h) in rapidity, ease of performance, and objectivity.

The role of complement in monoclonal antibody-mediated protection against virulent Semliki Forest virus

Monoclonal antibodies (MAs), specific for either the E1 or E2 glycoproteins of Semliki Forest virus (SFV), and belonging to various immunoglobulin subclasses (IgM, IgG2a, IgG2b and IgG3), effected lysis of SFV-infected L cells in co-operation with guinea-pig complement. In this antibody-dependent complement-mediated cytolysis (ADCMC) test, IgG1 MAs were not effective although these antibodies recognize the viral antigens on the surface of SFV-infected L cells. The latter was shown with horseradish peroxidase (HRPO)-labelled MAs in a direct enzyme immunoassay. The binding reactivities of HRPO-labelled MAs to infected L cells at selected time-intervals after infection correlated well with the amount of cytolysis in a parallel ADCMC test. Cytolysis was dependent on the duration of incubation with antibodies: more cytolysis was measured after a 4-hr incubation period with MA, starting at 4 hr after infection, compared to a 1-hr incubation period starting after 7 hr of infection. However, in the latter case (1-hr period) the amount of cytolysis measured correlated better to neutralization and/or protection by MAs than after the extended period (4 hr) of incubation. Complement (C3) depletion by cobra venom factor treatment led to a higher mortality and viraemia of mice prophylactically injected with critically protective doses of either the neutralizing MA UM 8.4 (IgM) or the non-neutralizing MA UM 4.2 (IgG2a). The results suggest a co-operative role of MA with complement in mediating protection against SFV. Passive immunization by administration of low amounts (0.1 micrograms/mouse) of neutralizing MA UM 5.1 resulted in protection of normal mice against a lethal infection with SFV. Mice immunosuppressed by cyclophosphamide were not protected by these doses. If the doses were increased however, these mice were protected both prophylactically and therapeutically. These results indicate that, using critical doses of MAs, an intact immune system ensures survival in normal mice after infection with virulent SFV.

Antigenic differences between virulent and avirulent strains of Semliki Forest viruses detected with monoclonal antibodies. Brief report

Eleven monoclonal antibodies (MAs) reacted strongly in an enzyme immunoassay with virulent Semliki Forest virus (SFV) replicating in L cell monolayers. Three MAs showed a considerably diminished reaction with an avirulent strain of SFV both in enzyme immunoassays and plaque reduction tests.

Adoptive transfer of immunity against virulent Semliki Forest virus with immune spleen cells from mice infected with avirulent Semliki Forest virus

This paper describes the minimal requirements to protect mice adoptively against challenge with virulent Semliki Forest virus (SFV). Early immune serum, from donor mice infected with an avirulent strain of SFV, contained mainly neutralizing IgM immunoglobulins. More of these antibodies (1.80 PND50 vs 0.06 PND50) were needed to protect recipient mice against intraperitoneal challenge (10 LD50 of SFV) than against subcutaneous challenge (7 LD50). Adoptive transfer experiments indicated that a minimum of 3 X 10(7) six-day immune spleen cells were also able to protect recipient mice against intraperitoneal challenge with 10 LD50 of SFV. Treatment of these donor cells with cytotoxic antisera and complement revealed both T- and B-lymphocytes were required for optimum adoptive immunity. Surviving recipients of either immune serum or immune spleen cells developed significantly less neutralizing antibodies than control mice. The lower antibody titres in protected mice might be related to either immune serum or immune spleen cell mediated restriction of virus replication; meaning a reduced antigenic stimulus in these mice compared to control mice.

Determination of inhibitory concentrations of antiviral agents in cell culture by use of an enzyme immunoassay with virus-specific, peroxidase-labeled monoclonal antibodies

An enzyme immunoassay (EIA) to determine 50% inhibitory concentrations of drugs which suppress Semliki Forest virus replication is described. Inhibition of virus replication was measured in L-cells, seeded as monolayers in 96-well plates by use of horseradish peroxidase-labeled monoclonal antibodies directed against the E1 glycoprotein of Semliki Forest virus. The antiviral agents tested were cycloheximide, tunicamycin, NH4Cl, and disodium cromoglycate. The 50% inhibitory concentration of these antiviral agents was arbitrarily defined as the concentration of drug, in culture medium, associated with 50% reduction of the control absorbance value measured on Semliki Forest virus-infected cells without drug in the culture fluid. Twenty-two hours after infection the 50% inhibitory concentrations of the drugs were 0.2 microgram/ml for cycloheximide, 0.8 microgram/ml for tunicamycin, 0.3 mg/ml for NH4Cl, and 4.9 mg/ml for disodium cromoglycate. These values are similar to those determined by others with conventional methods of virus quantification. This test is sensitive and easy to perform and therefore is suited for large-scale experiments.

Mechanisms of monoclonal antibody-mediated protection against virulent Semliki Forest virus

Both neutralizing and nonneutralizing immunoglobulin G2a monoclonal antibodies (MAs) directed against the E2 glycoprotein of Semliki Forest virus (SFV) protected mice prophylactically and therapeutically against virulent SFV infection. The neutralizing MAs, however, conferred protection to mice at lower doses than did nonneutralizing MAs. The antibody-dependent, complement-mediated cytolysis of SFV-infected L cells was effectuated by both kinds of antibodies, but again neutralizing MAs were more effective. Removal of the Fc part of the neutralizing MA UM 5.1 by pepsin digestion resulted in a 100-fold reduction of the neutralization titer (10(4) versus 10(6)) and a complete loss of its capacity to mediate antibody-dependent, complement-mediated cytolysis. Passive protection of infected mice occurred only after administration of relatively high doses of F(ab')2 of MA UM 5.1 (30.0 micrograms versus 0.1 microgram). F(ab')2 fragments prepared from the nonneutralizing MA UM 4.2 had lost their protective capacity completely. Surprisingly, the nonneutralizing MA UM 4.2 retarded virus growth in mouse fibroblasts (L cells), although inhibition was at much higher doses than with the neutralizing MA UM 5.1. Furthermore, both MAs promoted the uptake of virulent SFV in the Fc receptor-bearing WEHI-3 cells. The results suggest that nonneutralizing MAs protect mice not only by antibody-dependent, complement-mediated cytolysis but also by growth inhibition and enhanced uptake of SFV in the nonpermissive macrophages of BALB/c mice. This hypothesis is supported by the absence of viremia in recipients of nonneutralizing MA UM 4.2 at 24 h after infection.

Induction of delayed-type hypersensitivity to measles virus in mice

Intracutaneous injection of inactivated measles virus (MV) into hind footpads of BALB/c mice infected 5 to 11 days previously with MV produces a strong delayed-type hypersensitivity (DTH) response. Pretreatment of mice with cyclophosphamide (CP) results in a significantly stronger response. In CP-pretreated mice, the optimal infecting dose of live MV and the restimulating amount of inactivated MV are approximately 10(7) plaque-forming units and 2 micrograms/mouse, respectively. The optimal time after infection for measuring DTH to MV is 7 days, while the optimal CP-pretreatment concentration is 200 mg/kg. The DTH response generated by MV is specific and not caused by fetal calf serum or Vero cell antigens. MV DTH is transferable to uninfected mice with lymph node cells. Transfer of DTH is sensitive to treatment with anti-Thy 1.2 serum plus complement, indicating the response is T cell dependent. With this sensitive assay for measuring cell-mediated immunity to MV, it will now be possible to analyze T cell cross-reactivity among paramyxoviruses and assess viral cell-mediated immunity in mice infected with neuroadapted MV.

Identification of distinct antigenic determinants on Semliki Forest virus by using monoclonal antibodies with different antiviral activities

Fifteen monoclonal antibodies (MAs) directed against either the E1 or E2 glycoprotein of Semliki Forest virus (SFV) were characterized by immunoglobulin subclass, pI traject, hemagglutination inhibition, neutralization of infectious virus, and protection against virulent infection in mice. All MAs except UM8.4 (immunoglobulin M [IgM]) belonged to various subclasses of IgG and predominantly to IgG2a, but all were unique as indicated by their banding patterns in isoelectric focusing. Competitive binding assays with these MAs revealed the presence of at least six distinct antigenic determinants (epitopes) on the E1 glycoprotein and five epitopes on the E2 glycoprotein. Two of the epitopes on E1, as defined by the properties of the MAs, were associated with hemagglutination inhibition (E1c and E1d), three were associated with neutralization (E1a, E1b, and E1f), and five were associated in various degrees with protection (E1a, E1b, E1c, E1e, and E1f) of mice against virulent SFV infection. With the MAs against E2, the epitopes on E2 were similarly defined. Epitopes E2b and E2e were associated with hemagglutination inhibition, E2c and E2d were associated with neutralization, and three epitopes were associated with in vivo protection (E2a, E2c, and E2d). Furthermore, for each MA the relative avidity to purified SFV was determined with an enzyme-linked immunosorbent assay. The binding of some MAs to purified SFV was enhanced by a second MA. The relative avidities of individual MAs did not correlate with their neutralizing capacities. From the results, we suggest that the amino acid sequence which makes up determinant E2d and is recognized by the highly protective MA UM5.1 is an excellent candidate for the production of a synthetic vaccine.

Detection of Semliki Forest virus in cell culture by use of an enzyme immunoassay with peroxidase-labeled monoclonal antibodies specific for glycoproteins E1 and E2

Four noncompeting monoclonal antibodies (MA) directed against either the E1 (UM 8.64 and 8.139) or E2 (UM 8.55 and 8.73) glycoprotein of Semliki Forest virus were purified and labeled with horseradish peroxidase. Each enzyme-labeled MA was tested alone and in combination with others for its sensitivity to detect virus-infected cells. Semliki Forest virus-infected L cells seeded as monolayers in 96-well plates were screened for the virus after incubation with enzyme-labeled MA and a substrate. In this system single enzyme-labeled MA even at high dilution (10(3.0) to 10(4.5] were able to detect virus-infected cells. The sensitivity of the test could be enhanced by combining two noncompeting MA (10(4.5) to 10(5.0]. Combinations of three and four MA were less effective, due to high absorbance values for noninfected cells. The threshold of virus defection was between 10(5) and 10(6) PFU/ml. This test is sensitive and specific and therefore may be useful for diagnostic purposes.

The effect of liposomal charge on the neutralizing antibody response against inactivated encephalomyocarditis and Semliki Forest viruses

The primary neutralizing antibody response to encephalomyocarditis (EMC) virus and Semliki Forest virus (SFV) is enhanced by addition of either negatively or positively charged liposomes. The purified u.v. light inactivated viruses were merely mixed with liposomes and injected intraperitoneally (i.p.) into mice. In contrast, neutral liposomes were unable to enhance the primary response to these viruses. Furthermore primary immunization with inactivated SFV mixed with either neutral, positively or negatively charged liposomes was associated with an enhancement of the secondary humoral response after i.p. booster injection of mice with inactivated virus alone. But neutral liposomes seemed to be less effective in this respect than either positively or negatively charged liposomes.

Delayed-type hypersensitivity in mice after infection with avirulent Semliki Forest virus. Brief report

After subcutaneous infection of mice with Semliki Forest virus, a delayed-type hypersensitivity (DH) could be demonstrated by footpad swelling. Pretreatment with cyclophosphamide resulted in enhanced DH if neutralizing antibodies were undetectable in serum.

Genetic and antigenic requirements for induction of T helper cells for anti-Sendai virus-specific antibody production

T helper cells for the promotion of Sendai virus-specific antibody production were generated in vitro. They could be stimulated by infectious, UV light-inactivated or fusion-negative Sendai virus, which had to be presented by adherent cells. Induction of T helper cells was virus-specific and required H-2 IA region compatibility between T cells and antigen-presenting cells. Delivery of help to B lymphocytes was neither virus-specific nor H-2-restricted.

Dimethyl dioctadecyl ammoniumbromide as an adjuvant for delayed type hypersensitivity and cellular immunity against Semliki Forest virus in mice

Intracutaneous immunization of BALB/c mice with inactivated Semliki Forest virus mixed with the cationic, surface active lipid dimethyl dioctadecyl ammoniumbromide produced a strong enhancement of delayed type hypersensitivity without detectable antibodies in serum. Furthermore these mice were more protected against intraperitoneal challenge than normal immunized mice. This protection might be explained by an enhancement of cellular immunity against Semliki Forest virus. Dimethyl dioctadecyl ammoniumbromide by itself has no effect on footpad swelling, mortality and mean survival time.

Production of DTH in the mouse to influenza virus: comparison with conditions for stimulation of cytotoxic T cells

The kinetics of sensitization and elicitation of delayed-type hypersensitivity in mice to both infectious and non-infectious preparations of influenza virus was found to be similar to that of some protein antigens and to other viruses. Sensitization was achieved without added adjuvant. Maximum DTH was elicited in the footpad 6 days after sensitization. Adoptive transfer experiments showed that the effector cells were in the Ig-negative fraction of the spleen and were sensitive to anti-theta and complement. A comparison was made of conditions for the generation of DTH activity with cytotoxic T cells. The route of inoculation was important. With a high dose (10(3) HAU) of virus, subcutaneous inoculation was the most efficient and intravenous injection the least efficient for sensitizing for DTH, whereas the reverse was found for cytotoxic T-cell generation. Second, treatment of mice with cyclophosphamide (Cy) had differential effects. Preinjection of a large dose (200 mg/kg) into mice 2 days before sensitization with virus resulted in an increase in the DTH response and a 90% reduction in cytotoxic T-cell activity in the spleens of the treated mice. The Cy-injected mice had reduced (70%) anti-haemagglutinin levels compared with the controls. This may be the explanation for the enhanced DTH response, since transfer of specific antibody to sensitized mice before injection of the eliciting virus substantially reduced the DTH response. Pretreatment with Cy did not affect the generation of DTH effector cells, since spleen cells from these and control mice had similar levels of activity.

Specificity, Ly phenotype, and H-2 compatibility requirements of effector cells in delayed-type hypersensitivity responses to murine influenza virus infection

Delayed-type hypersensitivity (DTH) to infectious and to noninfectious (UV-irradiated) influenza A viral preparations was measured in mice by the increase in footpad swelling 24 h after injection of the eliciting virus. DTH mice sensitized with noninfectious virus was elicited only by virus that shared hemagglutinin specificity with the sensitizing virus, whereas footpad injection of a given A-strain virus (A/WSN) could elicit DTH in mice sensitized with a variety of infectious A-strain viruses, including some not sharing hemagglutinin or neuraminidase specificities. The effector T cells generated in mice sensitized with either form of virus were sensitive to anti-Ly 1.1 serum and complement, but not to anti-Ly 2.1 serum and complement. Adoptive transfer of DTH was H-2 restricted. With spleen cells from mice sensitized subcutaneously with either infectious or noninfectious virus, sharing of the IA region was both necessary and sufficient for successful transfer to occur. Cells recovered from infected mouse lungs, and secondary effector cells generated in vitro transferred DTH if injected into the footpad with the eliciting virus. The effector cells had the Ly 1 phenotype, and, in both cases, the cells were I restricted. These results contrast with earlier findings that transfer of DTH to lymphocytic choriomeningitis virus infection required K- or D-region sharing between donor and recipient. Thus, the earlier hypothesis that multiplying infectious agents such as viruses would "alter" K- or D-coded, rather than I-coded, structures is not generally correct.