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Identifying the Role of E2 Domains on Alphavirus Neutralization and Protective Immune Responses.

Weger-Lucarelli J, Aliota MT, Kamlangdee A, Osorio JE - PLoS Negl Trop Dis (2015)

Bottom Line: The alphavirus E2, the receptor-binding envelope protein, is considered to be the predominant target of the protective host immune response.Using chimeric viruses, it was determined that the alphavirus E2 domain B was the critical target of neutralizing antibodies in both mice and humans.Therefore, chimeric viruses may have more relevance for vaccine discovery than peptide-based approaches, which only detect linear epitopes.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathobiological Sciences, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.

ABSTRACT

Background: Chikungunya virus (CHIKV) and other alphaviruses are the etiologic agents of numerous diseases in both humans and animals. Despite this, the viral mediators of protective immunity against alphaviruses are poorly understood, highlighted by the lack of a licensed human vaccine for any member of this virus genus. The alphavirus E2, the receptor-binding envelope protein, is considered to be the predominant target of the protective host immune response. Although envelope protein domains have been studied for vaccine and neutralization in flaviviruses, their role in alphaviruses is less characterized. Here, we describe the role of the alphavirus E2 domains in neutralization and protection through the use of chimeric viruses.

Methodology/principal findings: Four chimeric viruses were constructed in which individual E2 domains of CHIKV were replaced with the corresponding domain from Semliki Forest virus (SFV) (ΔDomA/ΔDomB/ΔDomC/ ΔDomA+B). Vaccination studies in mice (both live and inactivated virus) revealed that domain B was the primary determinant of neutralization. Neutralization studies with CHIKV immune serum from humans were consistent with mouse studies, as ΔDomB was poorly neutralized.

Conclusions/significance: Using chimeric viruses, it was determined that the alphavirus E2 domain B was the critical target of neutralizing antibodies in both mice and humans. Therefore, chimeric viruses may have more relevance for vaccine discovery than peptide-based approaches, which only detect linear epitopes. This study provides new insight into the role of alphavirus E2 domains on neutralization determinants and may be useful for the design of novel therapeutic technologies.

No MeSH data available.


Related in: MedlinePlus

Representative histopathology of spleen and brain of live-virus vaccinated C57bl/6 mice post-challenge.Mice previously infected with 105 PFU of CHIK or chimeric viruses (ΔDomA, ΔDomB or ΔDomC) were challenged with 105 PFU of SFV. Surviving mice were euthanized and spleens and brains were harvested followed by processing for Hematoxylin and Eosin (H&E) staining. A-F. Spleens at 10x magnification. The scale bars represent 100 μM. G-L. Hippocampal neurons at 25x magnification. The scale bar represents 50 μM. Arrows signify neuron degeneration.
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pntd.0004163.g003: Representative histopathology of spleen and brain of live-virus vaccinated C57bl/6 mice post-challenge.Mice previously infected with 105 PFU of CHIK or chimeric viruses (ΔDomA, ΔDomB or ΔDomC) were challenged with 105 PFU of SFV. Surviving mice were euthanized and spleens and brains were harvested followed by processing for Hematoxylin and Eosin (H&E) staining. A-F. Spleens at 10x magnification. The scale bars represent 100 μM. G-L. Hippocampal neurons at 25x magnification. The scale bar represents 50 μM. Arrows signify neuron degeneration.

Mentions: To assess the role of E2 domains in protection, vaccinated mice were challenged with 105 PFU wild-type SFV via the same route two months post vaccination. To evaluate the protective efficacy of the chimeric viruses, mouse mortality was monitored following challenge. All mock vaccinated mice quickly succumbed to infection (Fig 2b). In contrast, all other mice survived challenge with no overt clinical signs. Because mice survived infection without overt clinical signs, we undertook a comparative histological analysis of the spleen and brain five days post infection, specifically surveying for obvious morphological changes as the result of secondary challenge. Based on previous literature, particular attention was paid to lymphocyte depletion in the spleen and degeneration of hippocampal neurons in the brain [36]. Examination of H&E sections of mouse spleen did not reveal obvious changes in splenic architecture or lymphocyte levels (Fig 3a) associated with inoculation of diluent alone. As compared to mock inoculated controls, pathology was detected in spleens of all mice vaccinated with chimeric viruses and then challenged with SFV, albeit to a lesser degree than mice that were mock vaccinated and then challenged with SFV (Fig 3b–3f). Spleens of mock-vaccinated mice exhibited massive lymphocyte depletion (Fig 3f). Mice vaccinated with CHIKV displayed moderate levels of lymphocyte depletion following SFV challenge (Fig 3b). In contrast, ΔDomA and ΔDomB-vaccinated mice experienced mild lymphocyte depletion after SFV challenge (Fig 3c and 3d). Examination of hippocampal neurons of challenged mice revealed that vaccination with ΔDomB appeared to protect mice from neuro-invasion of SFV, i.e., neurons were almost completely intact (Fig 3g–3j). Considerable lesions in the hippocampus were observed in all other groups and mock-vaccinated mice exhibited severe neuron degeneration in the hippocampus (Fig 3f).


Identifying the Role of E2 Domains on Alphavirus Neutralization and Protective Immune Responses.

Weger-Lucarelli J, Aliota MT, Kamlangdee A, Osorio JE - PLoS Negl Trop Dis (2015)

Representative histopathology of spleen and brain of live-virus vaccinated C57bl/6 mice post-challenge.Mice previously infected with 105 PFU of CHIK or chimeric viruses (ΔDomA, ΔDomB or ΔDomC) were challenged with 105 PFU of SFV. Surviving mice were euthanized and spleens and brains were harvested followed by processing for Hematoxylin and Eosin (H&E) staining. A-F. Spleens at 10x magnification. The scale bars represent 100 μM. G-L. Hippocampal neurons at 25x magnification. The scale bar represents 50 μM. Arrows signify neuron degeneration.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4608762&req=5

pntd.0004163.g003: Representative histopathology of spleen and brain of live-virus vaccinated C57bl/6 mice post-challenge.Mice previously infected with 105 PFU of CHIK or chimeric viruses (ΔDomA, ΔDomB or ΔDomC) were challenged with 105 PFU of SFV. Surviving mice were euthanized and spleens and brains were harvested followed by processing for Hematoxylin and Eosin (H&E) staining. A-F. Spleens at 10x magnification. The scale bars represent 100 μM. G-L. Hippocampal neurons at 25x magnification. The scale bar represents 50 μM. Arrows signify neuron degeneration.
Mentions: To assess the role of E2 domains in protection, vaccinated mice were challenged with 105 PFU wild-type SFV via the same route two months post vaccination. To evaluate the protective efficacy of the chimeric viruses, mouse mortality was monitored following challenge. All mock vaccinated mice quickly succumbed to infection (Fig 2b). In contrast, all other mice survived challenge with no overt clinical signs. Because mice survived infection without overt clinical signs, we undertook a comparative histological analysis of the spleen and brain five days post infection, specifically surveying for obvious morphological changes as the result of secondary challenge. Based on previous literature, particular attention was paid to lymphocyte depletion in the spleen and degeneration of hippocampal neurons in the brain [36]. Examination of H&E sections of mouse spleen did not reveal obvious changes in splenic architecture or lymphocyte levels (Fig 3a) associated with inoculation of diluent alone. As compared to mock inoculated controls, pathology was detected in spleens of all mice vaccinated with chimeric viruses and then challenged with SFV, albeit to a lesser degree than mice that were mock vaccinated and then challenged with SFV (Fig 3b–3f). Spleens of mock-vaccinated mice exhibited massive lymphocyte depletion (Fig 3f). Mice vaccinated with CHIKV displayed moderate levels of lymphocyte depletion following SFV challenge (Fig 3b). In contrast, ΔDomA and ΔDomB-vaccinated mice experienced mild lymphocyte depletion after SFV challenge (Fig 3c and 3d). Examination of hippocampal neurons of challenged mice revealed that vaccination with ΔDomB appeared to protect mice from neuro-invasion of SFV, i.e., neurons were almost completely intact (Fig 3g–3j). Considerable lesions in the hippocampus were observed in all other groups and mock-vaccinated mice exhibited severe neuron degeneration in the hippocampus (Fig 3f).

Bottom Line: The alphavirus E2, the receptor-binding envelope protein, is considered to be the predominant target of the protective host immune response.Using chimeric viruses, it was determined that the alphavirus E2 domain B was the critical target of neutralizing antibodies in both mice and humans.Therefore, chimeric viruses may have more relevance for vaccine discovery than peptide-based approaches, which only detect linear epitopes.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathobiological Sciences, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.

ABSTRACT

Background: Chikungunya virus (CHIKV) and other alphaviruses are the etiologic agents of numerous diseases in both humans and animals. Despite this, the viral mediators of protective immunity against alphaviruses are poorly understood, highlighted by the lack of a licensed human vaccine for any member of this virus genus. The alphavirus E2, the receptor-binding envelope protein, is considered to be the predominant target of the protective host immune response. Although envelope protein domains have been studied for vaccine and neutralization in flaviviruses, their role in alphaviruses is less characterized. Here, we describe the role of the alphavirus E2 domains in neutralization and protection through the use of chimeric viruses.

Methodology/principal findings: Four chimeric viruses were constructed in which individual E2 domains of CHIKV were replaced with the corresponding domain from Semliki Forest virus (SFV) (ΔDomA/ΔDomB/ΔDomC/ ΔDomA+B). Vaccination studies in mice (both live and inactivated virus) revealed that domain B was the primary determinant of neutralization. Neutralization studies with CHIKV immune serum from humans were consistent with mouse studies, as ΔDomB was poorly neutralized.

Conclusions/significance: Using chimeric viruses, it was determined that the alphavirus E2 domain B was the critical target of neutralizing antibodies in both mice and humans. Therefore, chimeric viruses may have more relevance for vaccine discovery than peptide-based approaches, which only detect linear epitopes. This study provides new insight into the role of alphavirus E2 domains on neutralization determinants and may be useful for the design of novel therapeutic technologies.

No MeSH data available.


Related in: MedlinePlus