Role of T-cells, virus neutralising antibodies and complement-mediated antibody lysis in the immune response against equine herpesvirus type-1 (EHV-1) infection of C3H (H-2k) and BALB/c (H-2d) mice

Immune and inflammatory response in horse vaccinated against equine herpesviruses 1 (EHV-1) and 4 (EHV-4) assessed by serum protein electrophoretic pattern and leukocyte population

Protection against infectious diseases can be obtained with vaccines generating immunogenic response through a combination of humoral and cellular immunity. In this study haematological and serum protein electrophoretic profiles of horses vaccinated against herpesvirus 1 (EHV-1) and 4 (EHV-4) were evaluated. Blood samples were collected from 16 horses before (T0), after 24h, 48h, 72h, 1st week, 2nd week and 3rd week (T1I, T2I, T3I, T7I, T14I and T21I) from the first EHV vaccine-dose administration as well as before (TPRE_II), and after 24h, 48h, 72h, 1st week, 2nd week, 3rd week and 4th week (T1II, T2II, T3II, T7II, T14II, T21II and T28II) from the EHV vaccine-booster. Total leukocyte values increased at T1I, T1II, T3II and T28II compared to T0 (P<0.01). Higher lymphocytes and lower neutrophils values were found after first vaccine-dose and vaccine-booster administration compared to the T0 (P<0.01). Monocytes showed higher values at T14II than T0 (P<0.01). Higher serum values of total proteins, α1-, α-2-, β1-, β2- and γ-globulins were found in horses after first vaccine-dose and vaccine-booster administration (P<0.01). Gathered results suggest that horses vaccinated against EHV1 and EHV-4 exhibited a dynamic change of WBC, lymphocytes, neutrophils and monocytes. Moreover, the analysis of serum electrophoresis pattern suggested that EHV vaccination induced the development of inflammation and antibody response in vaccinated horses as highlighted by the increase of α-, β- and γ-globulin fractions. These changes probably reflect the systemic immunological adaptation of animals to EHV vaccine.

Diverse pathogenicity of equine herpesvirus 1 (EHV-1) isolates in CBA mouse model

The pathogenicity of equine herpesvirus 1 (EHV-1) isolates of Japan were evaluated by using the CBA mouse model. CBA mice were inoculated with eight Japanese EHV-1 strains (89c1, 90c16, 90c18, 97c11, 98c12, 00c19, 01c1 and HH-1) and one British strain (Ab4p). 89c1 caused slight body weight loss and nervous signs in mice at 8 days post infection (dpi). Severe weight loss and nervous signs were observed in mice inoculated with Ab4p at 6 dpi. The other strains did not cause apparent clinical signs. Infectious viruses were recovered from the lungs of all groups at 2 dpi. Histopathological analysis revealed interstitial pneumonia in the lungs of all mice inoculated with EHV-1. Encephalitis or meningoencephalitis was observed in the brains of mice inoculated with 89c1, 90c18, 97c11, 98c12, 01c1 and Ab4p. Japanese EHV-1 strains showed low pathogenicity in CBA mice, whereas the sequential affects of infection are similar to those of the highly pathogenic strain Ab4p. These results suggest that field isolates of EHV-1 have varying degrees of pathogenicity in CBA mice.

CCL3 and viral chemokine-binding protein gg modulate pulmonary inflammation and virus replication during equine herpesvirus 1 infection

CCL3 is a proinflammatory chemokine that mediates many of the cellular changes occurring in pulmonary disease. Here, CCL3(-/-) mice were used to investigate the role of this chemokine during respiratory herpesvirus infection. Compared to wild-type mice, CCL3(-/-) mice infected with the alphaherpesvirus equine herpesvirus 1 (EHV-1) displayed reduced body weight loss but had higher pulmonary viral loads. Lungs from infected CCL3(-/-) mice suffered a milder interstitial pneumonia, and fewer immune cells were recovered from the pulmonary airways after infection. We could also demonstrate that herpesvirus-encoded chemokine-binding glycoprotein G (gG) was capable of inhibiting the chemotactic functions of CCL3. This CCL3-mediated chemotaxis, however, was restored in the presence of gG-specific antibodies, which puts into question the advertised use of gG deletion mutants as marker vaccines. In summary, we concluded that CCL3 is a major player in controlling herpesvirus replication in the target organ, the lung, and does so by evoking a strong inflammatory response. The immunomodulatory activity of CCL3 is balanced by the expression of viral gG, whose chemokine-binding activity is mitigated in secondary infections by the production of anti-gG antibodies.

Pathogenicity and immunogenicity of equine herpesvirus type 1 mutants defective in either gI or gE gene in murine and hamster models

To develop a live vaccine for equine herpesvirus type 1 (EHV-1), two EHV-1 mutants containing no heterogeneous DNA, DeltagI and DeltagE, were constructed with deletions in the open reading frame of either glycoprotein I (gI) or E (gE), respectively. In equine cell culture, deletion mutants formed smaller plaques than the parental and revertant viruses, but the one-step growth patterns of the deletion mutants and the parental strain were approximately the same. These results suggest that both gI and gE contribute to the ability of EHV-1 to spread directly from cell-to-cell, but that these glycoproteins are not required for viral growth in vitro. Mice and hamsters inoculated intranasally with these mutants showed no clinical signs, and continued to gain weight, whereas those inoculated with the parental virus exhibited a reduction in mean body weight. Furthermore, nervous manifestations were observed in hamsters inoculated with the parental virus. These results suggest that gI and gE have an important role in EHV-1 virulence including neurovirulence in experimental animal models. On the other hand, serum neutralizing antibodies were detected in mice immunized with DeltagI or DeltagE at two weeks after inoculation. Following challenge with the parental virus, DeltagI- or DeltagE-immunized mice were able to clear parental virus from their lungs faster than mock-immunized mice. These results suggest that the EHV-1 mutants defective in gI and in gE are attenuated but have ability to elicit immune responses in inoculated mice that contribute to virus clearance.

Intercellular Adhesion Molecule-1 (ICAM-1) and Lymphocyte Function-associated Antigen-1 (LFA-1) Contribute to the Elimination of Equine Herpesvirus Type 1 (EHV-1) from the Lungs of Intranasally Infected BALB/c Mice

The role of intercellular adhesion molecule-1 (ICAM-1) and lymphocyte function-associated antigen-1 (LFA-1) on equine herpesvirus type 1 (EHV-1) infection in BALB/c mice produced by intranasal inoculation was studied. Infected mice were found to lose bodyweight (BW) during the acute phase of infection (i.e., within 1 week of inoculation) but to regain it during the convalescent phase. The intraperitoneal administration of monoclonal antibodies (mAbs) against ICAM-1 and LFA-1 one day before EHV-1 infection reduced the BW loss in the acute phase and retarded the recovery of BW in the convalescent phase. When mice pretreated with mAbs were killed 21 days after infection, the epithelial cells of the bronchi and bronchioles were found to contain viral antigens and to show degeneration and necrosis. In non-pretreated control mice, no viral antigens were detected and lesions were mild or absent. It was concluded that ICAM-1 and LFA-1 contributed to the elimination of EHV-1 from the lung, and to recovery. These findings may be relevant to EHV-1 infection in the horse.

Enhanced atherogenesis is not an obligatory response to systemic herpesvirus infection in the apoE-deficient mouse: comparison of murine gamma-herpesvirus-68 and herpes simplex virus-1

Viral and bacterial infectious agents have been implicated in the etiology of atherosclerosis. We have previously shown that a gamma-herpesvirus can accelerate atherosclerosis in the apolipoprotein E-deficient (apoE-/-) mouse. To address whether a virally induced systemic immune response is sufficient to trigger enhanced atheroma formation, we infected apoE-/- mice with murine gamma-herpesvirus-68 (MHV-68) or herpes simplex virus-1 (HSV-1). In this study, we show that both viruses were able to induce a cell-mediated and humoral immune response in the apoE-/- mouse, which was sustained over a period of 24 weeks. Although intranasal or intraperitoneal infection with MHV-68 induced similar levels of virus-specific IgG1 and IgG2a antibodies in the serum of apoE-/- mice, those infected with HSV-1 showed higher anti-HSV-1 IgG2a compared with IgG1 antibody levels. In addition, viral message was not detected in the aortas of HSV-1-infected animals, whereas we have shown previously that MHV-68 mRNA can be detected in the aortas of infected mice as early as 5 days after infection. Compared with control mice, apoE-/- mice infected with MHV-68 showed accelerated atherosclerosis, whereas mice infected with HSV-1 did not. These data indicate that a systemic immune response to any particular infectious agent is insufficient to induce enhanced atherosclerosis in the apoE-/- mouse and point to specific infections or immune mechanisms that might be essential for virally enhanced atherogenesis.

Solid matrix-antibody-antigen complexes incorporating equine herpesvirus 1 glycoproteins C and D elicit anti-viral immune responses in BALB/c (H-2K(d)) and C3H (H-2K(k)) mice

Glycoproteins C and D (gC and gD) derived from equine herpesvirus 1 (EHV-1)-infected cells were incorporated into individual solid matrix-antibody-antigen (SMAA) complexes and administered to BALB/c (H-2K(d)) and C3H (H-2K(k)) mice. Antibodies against each of the glycoproteins were produced that neutralised virus infectivity and mediated the lysis of EHV-1-infected target cells in the presence of complement. Immunoglobulin (Ig)G2b was the predominant antibody isotype produced in BALB/c mice against gC, while equal amounts of IgG2a/2b were found in the serum of C3H mice (indicative of a T-helper(1) response). Glycoprotein D immunisation elicited predominantly an IgG1 response in BALB/c mice (indicative of a T-helper(2) response) and an IgG2a/2b response in C3H mice. EHV-1-specific local and systemic T-cell proliferative responses were detected in vitro following administration of SMAA complexes. Suppression of the local T-cell response was seen following virus challenge of mice immunised with SMAA gC. SMAA gD provided some protection against intranasal EHV-1 challenge. These data show that the SMAA system is an effective way of presenting subviral components to the immune system and further emphasises the importance of including glycoprotein D as a component of a subunit EHV-1 vaccine.

Severe murine lung immunopathology elicited by the pathogenic equine herpesvirus 1 strain RacL11 correlates with early production of macrophage inflammatory proteins 1alpha, 1beta, and 2 and tumor necrosis factor alpha

The CBA mouse model was used to investigate the immunopathology induced in the lung by the pathogenic equine herpesvirus 1 (EHV-1) strain RacL11 in comparison to infection with the attenuated vaccine candidate strain KyA. Intranasal infection with KyA resulted in almost no inflammatory infiltration in the lung. In contrast, infection with the pathogenic RacL11 strain induced a severe alveolar and interstitial inflammation, consisting primarily of lymphocytes, macrophages, and neutrophils. Infection with either EHV-1 strain resulted in the accumulation of similar numbers and ratios of CD4 and CD8 T lymphocytes in the lung and bronchoalveolar lavage (BAL) fluid. Further analysis of these T-cell populations revealed identical EHV-1-specific cytotoxic T-lymphocyte responses. RNase protection analysis of RNA isolated from the BAL fluid of RacL11-infected mice on day 3 postinfection revealed much higher levels of RNA specific for macrophage inflammatory protein 1alpha (MIP-1alpha), MIP-1beta, and MIP-2 than were observed for KyA-infected mice. Furthermore, significantly higher levels of transcripts specific for tumor necrosis factor alpha were induced on day 3 postinfection with RacL11 compared with KyA. These findings suggest that the early production of proinflammatory beta chemokines plays a major role in the severe, most often lethal, respiratory inflammatory response induced by the pathogenic EHV-1 strain RacL11.

Herpesvirus infection accelerates atherosclerosis in the apolipoprotein E-deficient mouse

BACKGROUND

Human herpesviruses have been implicated but not proven to be involved in the etiology of atherosclerosis. To determine whether there is a causal relationship, the effect of herpesvirus infection on the development of atherosclerosis was assessed in the apolipoprotein E-deficient (apoE-/-) mouse.

METHODS AND RESULTS

In the present study, 3- to 4-week-old apoE-/- mice were infected with murine gamma-herpesvirus-68 (MHV-68). Atheroma formation was accelerated over a 24-week period in infected apoE-/- mice compared with control uninfected apoE-/- mice. Acceleration of atherosclerosis was reduced by antiviral drug administration. Histological analysis of the atheromatous plaques showed no difference between lesions of infected and control mice. Viral mRNA was present in the aortas of infected mice before lesion development on day 5 after infection. This suggests that the virus may initiate endothelial injury, which is believed to be an early event in the development of atherosclerosis. Therefore, the virus may play a direct role in atherosclerosis rather than be an "innocent bystander."

CONCLUSIONS

These data demonstrate that a gamma-herpesvirus can accelerate atherosclerosis in the apoE-/- mouse. This study provides the first report of a murine model in which to study the causative role of herpesvirus infection in the development of atherosclerosis.

Quantitation of virus-specific classes of antibodies following immunization of mice with attenuated equine herpesvirus 1 and viral glycoprotein D

The antibody responses of CBA/J mice infected intranasally (i.n.) with either the attenuated KyA strain or the pathogenic RacL11 strain of equine herpesvirus 1 (EHV-1) or immunized with recombinant glycoprotein D (rgD) were investigated using the ELISPOT assay to measure EHV-1-specific antibody-secreting cells (ASC) in the regional lymphoid tissue of the respiratory tract. IgG, IgA, and IgM ASC specific for EHV-1 were detected in the mediastinal lymph nodes (MLN) and lungs 2 weeks after i.n. infection with EHV-1 strain KyA or RacL11, or immunization with heat-killed KyA or rgD. EHV-1-specific ASC were present in the MLN and lungs at 4 and 8 weeks, but declined in frequency by fivefold in the lung at 8 weeks. However, i.n. immunized (2 x 10(6) pfu KyA or 50 microgram rgD/mouse) mice infected at 8 weeks with pathogenic EHV-1 RacL11 resisted challenge and showed eight- and tenfold increases in MLN ASC and lung ASC, respectively, by 3 days after challenge. In contrast to the intranasal route of immunization, intraperitoneal immunization yielded ASC frequencies in the MLN and lungs that were only slightly above those of nonimmunized control mice. These data indicate that immunization with infectious or heat-killed EHV-1 KyA, or rgD, induces significant levels of virus-specific ASC both in the MLN and lungs, a specific memory B-cell response, and long-term protective immunity. The finding that the numbers of ASC induced by the pathogenic strain versus the attenuated strain of EHV-1, which were virtually identical, indicated that the ability to generate a B-cell response is independent of and does not contribute to EHV-1 virulence.

Comparison of the pathogenesis of acute equine herpesvirus 1 (EHV-1) infection in the horse and the mouse model: a review

The mouse models of the respiratory and abortion forms of equine herpesvirus 1 (EHV-1) infection have been used to investigate the vaccine potential of various EHV-1 immunogens, the effect of antiviral agents on EHV-1 infection and the pathogenicity of EHV-1 strain variants and deletion or insertional mutants. This review examines the similarities and differences in the pathogenesis of primary EHV-1 infection in the natural host, the horse, and in the mouse by comparing tissue tropism, clinical signs of infection, the effects of EHV-1 on pregnancy, haematological changes following infection, viral clearance, histopathology and latency. The evidence suggests that the mouse model provides a valid method for investigation of virological and histopathological aspects of EHV-1-induced disease in the horse. However, the extent to which useful and valid comparisons and extrapolations can be made of immunological parameters from mouse to horse is yet to be determined.

DNA-mediated immunization with glycoprotein D of equine herpesvirus 1 (EHV-1) in a murine model of EHV-1 respiratory infection

DNA-mediated immunization was assessed in a murine model of equine herpesvirus 1 (EHV-1) respiratory infection. A single intramuscular injection with plasmid DNA encoding EHV-1 glycoprotein D (EHV-1 gD), including its predicted C-terminal membrane anchor sequence, induced a specific antibody response detectable by 2 weeks and maintained through 23 weeks post injection. A second injection at 4 weeks markedly enhanced the antibody response and all EHV-1 gD-injected mice developed neutralizing antibodies. A lymphocyte proliferative response to whole EHV-1 was observed and a predominance of IgG2a antibodies after DNA injection was consistent with the generation of a type 1 helper T-cell (Th1) response. Following intranasal challenge with EHV-1, mice immunized with EHV-1 gD DNA were able to clear virus significantly more rapidly from lung tissue and showed reduced lung pathology, in comparison to control mice.

Primary and challenge infection of mice with equine herpesvirus 1, strain HSV25A

Clinical signs, haematology, lymphocyte subset analysis, viral clearance, lung histopathology and humoral and cell-mediated (CMI) immune responses were monitored throughout the acute and convalescent phases of infection in groups of BALB/c mice infected intranasally with equine herpesvirus 1 (EHV-1), strain HSV25A. Primary infection caused a leucocytosis due to a neutrophilia during days 1 and 2 post-infection (pi) and a B lymphocytosis at day 1 pi. Serum ELISA antibodies were detected by 7 days pi and neutralising antibodies by 2 weeks pi. Mice infected with EHV-1 were not protected against disease when challenged with EHV-1 12 weeks later. However, viral clearance from lungs was significantly faster and the antibody response was markedly enhanced within the first few days of challenge infection. A CMI response was detected by 5 days after primary infection, but the level of responsiveness was not increased by challenge infection, although the lungs of challenged mice had markedly increased numbers of mononuclear cells around blood vessels and bronchioles. Specific antibodies to glycoprotein (g) B were detected by 2 weeks pi, 4 weeks earlier than the detection of antibodies to gC and 10 weeks before those to gD. The primary response was relatively short-lived with neither ELISA antibody nor lymphocyte proliferation was evident by 6 months pi.

Characterization of the cytolytic T-lymphocyte response to a candidate vaccine strain of equine herpesvirus 1 in CBA mice

The cytolytic T-lymphocyte (CTL) response to respiratory infection with equine herpesvirus 1 (EHV-1) in CBA (H-2(k)) mice was investigated. Intranasal (i.n.) inoculation of mice with the attenuated EHV-1 strain KyA resulted in the generation of a primary virus-specific CTL response in the draining mediastinal lymph nodes 5 days following infection. EHV-1-specific CTL could be restimulated from the spleen up to 26 weeks after the resolution of infection, indicating that a long-lived memory CTL population was generated. Depletion of CD8+ T cells by treatment with antibody and complement prior to assay eliminated CTL activity from both primary and memory populations, indicating that cytolytic activity in this model was mediated by class I major histocompatibility complex-restricted, CD8+ T cells. A single i.n. inoculation with KyA induced protective immunity against infection with the pathogenic EHV-1 strain, RacL11. The adoptive transfer of splenocytes from KyA-immune donors into sublethally irradiated recipients resulted in a greater than 250-fold reduction in RacL11 in the lung. The elimination of both CD4+ and CD8+ T cells from the transferred cells abrogated clearance of RacL11, while the selective depletion of either subpopulation alone had little effect. These results suggested that both lymphocyte subpopulations contribute to viral clearance, with either subpopulation alone being sufficient.

In situ study on the pathogenesis and immune reaction of equine herpesvirus type 1 (EHV-1) infections in mice

The mouse model was used to study the pathogenesis of equine herpesvirus type 1 (EHV-1) after primary and secondary intranasal infections. Within a few hours after infection, EHV-1 was found in nasal and olfactorial epithelium and sub-epithelial cells of the respiratory mucosa, but antigen-specific immune cells were never detected. Next to the lung, EHV-1 was transmitted early and directly to the brain, both via the olfactory route and the trigeminal nerve, but traces of degenerative or inflammatory processes were not detected there. In the lung, the immune cells residing or invading the parenchyma did not contain viral DNA or proteins. The primary immune response in the lungs was an alveolar and interstitial inflammation, dominated by the sequential appearance of neutrophils and macrophages, while the number of T and B lymphocytes remained unaltered. Within 24 hr after re-infection, lymphocytes accumulated around the blood vessels, outnumbering monocytes more than twofold, without neutrophils appearing. The lymphocytes comprised of little more B than T cells and the T cells were predominantly CD8+ cells. Those and B cells infiltrated the parenchyma. These results show the route of virus distribution and demonstrate the lack of antigen-specific immune cells in the lungs of mice after primary intranasal infection with EHV-1.

High level expression of equine herpesvirus 1 glycoproteins D and H and their role in protection against virus challenge in the C3H (H-2Kk) murine model

N and C-terminal truncated forms of equine herpesvirus 1 (EHV 1) glycoproteins gD and gH were expressed in baculovirus resulting in the production of secreted recombinant proteins. A carboxy-terminal histidine tag was included on each of the genes for protein isolation by nickel affinity chromatography. Recombinant gD was recognized by three gD specific monoclonal antibodies, 20C4, 5H6 and F3132. F3132 is a conformationally dependent monoclonal antibody with virus neutralizing activity. Expression of gH was confirmed by reacting the protein with the gH peptide specific antiserum R319. The truncated gD gene was also expressed as a beta-galactosidase fusion protein which was purified from E. coli by nickel affinity chromatography. C3H mice were inoculated with purified recombinant gD or gH or insect cells which had been infected with recombinant baculoviruses. Mice were subsequently challenged with EHV 1. Purified recombinant baculovirus gD provided the most protection and produced high levels of virus neutralizing antibodies. The gD fusion protein was less effective at protecting mice and insect cells infected with either of the recombinant baculoviruses or purified recombinant gH were poor at conferring protection. The results emphasize the importance of using purified proteins in vaccine formulations and of including EHV 1 gD as a component of a subunit vaccine.

The production of a truncated form of baculovirus expressed EHV-1 glycoprotein C and its role in protection of C3H (H-2Kk) mice against virus challenge

A truncated form of the equine herpesvirus 1 (EHV-1) glycoprotein C (gC) gene was expressed in baculovirus. The gC signal sequence was substituted with the honeybee melittin signal sequence and the transmembrane region was replaced with a histidine tag. The recombinant virus produced high levels of gC in both the cells and supernatants of infected cells. The protein was present by 24 h and maximal secretion occurred at 96 h post-infection. The recombinant protein was antigenically authentic as shown by its reaction with each of a panel of individual monoclonal antibodies specific for the five distinct antigenic sites on EHV-1 gC. Recombinant gC was purified from the supernatant of infected cells by immuno-affinity chromatography and used to immunize C3H (H-2Kk haplotype) mice. This incurred a gC specific antibody response against both the recombinant protein and EHV-1 gC. 'Pepscan' analysis showed that the gC specific antibodies in serum from these mice reacted with the same epitopes on gC as those recognized by antibodies in convalescent equine sera (i.e. antibodies were specific to antigenic sites one and five). A third previously unrecognized antibody binding site at the carboxyl terminus was also detected (Antibody binding domain I). A T-cell proliferative response against EHV-1 was detected in splenocyte populations taken from vaccinated mice. Further, the recovery of virus from the lungs and turbinates following challenge of mice with EHV-1 was significantly reduced. These findings indicate that baculovirus expressed gC may contribute significantly to a subunit vaccine preparation aimed at protecting horses from EHV-1 infection.

The expression of the proteins of equine herpesvirus 1 which share homology with herpes simplex virus 1 glycoproteins H and L

Several expression systems were used in studies aimed at characterizing the equine herpesvirus 1 (EHV-1) glycoprotein H and L homologues of HSV-1 (EHV-1 gH and gL) and the products were compared to the authentic proteins synthesized in virus infected cells. Using an in vitro transcription/translation system two gH species were detected (an unprocessed 89 kDa and a processed 116 kDa product). Three low molecular weight proteins were found in the case of gL (21.8 kDa, 22.9 kDa and 26.9 kDa) and these showed a slight reduction in mobility on the addition of microsomal membranes to the reactions. A gL fusion protein was produced in pGEX-2T, expression being confirmed by Western blotting using a gL-specific antiserum raised against a peptide incorporating the 13 carboxyl terminal amino acids of the protein. A gH specific peptide antiserum precipitated both gH and two smaller proteins from EHV-1 infected cells thought to be two forms of gL. Insect cells infected with gH or gL baculovirus recombinants were used to vaccinate C3H (H-2k) mice. Some protection against EHV-1 infection was conferred to the gH inoculated mice. The results will enable further studies on the importance of the gH and gL interaction in the pathogenesis of EHV-1 to be evaluated and their potential in contributing to a subunit vaccine to be assessed.