CMV Pp65
Description
Role in Immune Evasion and Modulation
CMV pp65 actively subverts host defenses through:
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NK cell inhibition: Direct interaction with NKp30 receptor to suppress cytotoxicity
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Interferon suppression: Blocks IRF-3 activation, dampening IFN-β response within 2 hours post-infection
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MHC class II downregulation: Reduces antigen presentation to CD4⁺ T cells
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Cytokine modulation: Alters chemokine profiles to evade immune detection
Immunodominance in T Cell Responses
CMV pp65 drives robust CD4⁺ and CD8⁺ T cell responses:
Key Findings:
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CD8⁺ T cells:
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CD4⁺ T cells:
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Polyfunctional cytotoxicity:
| Response Metric | CD8⁺ T Cells | CD4⁺ T Cells |
|---|---|---|
| IL-2 production | 4.6% | 19% |
| IFN-γ secretion | 89% | 78% |
| TNF-α co-expression | 82% | 71% |
Diagnostic Applications
CMV pp65 antigenemia assays remain clinically relevant despite PCR advancements:
Limitations:
Adoptive T Cell Therapy
Vaccine Platforms
Emerging Research Directions
Product Specs
Strongly reacts with human CMV positive serum.
Q&A
Basic Research Questions
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What is CMV pp65 and what is its biological significance?
CMV pp65 (also known as ppUL83) is a major structural protein and one of the most abundant components in the cytomegalovirus virion. It plays critical roles in viral replication and immune evasion mechanisms. Research has demonstrated that pp65 dampens the virion-mediated interferon-like response in cells following CMV penetration . Specifically, pp65 subverts the activation of the transcription factor IRF-3 within early times after infection, thereby undermining the host antiviral response .
While pp65 is nonessential for in vitro CMV growth, its immunomodulatory functions support a potential role in primary and/or persistent infection in vivo . Deletion studies with rhesus CMV lacking both pp65 orthologs (RhCMVΔpp65ab) have shown that absence of pp65 slightly reduces growth in vitro and increases defective particle formation, though the protein composition of secreted virions remains largely unchanged .
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How does the pp65 antigenemia assay function as a diagnostic tool?
The pp65 antigenemia assay is a widely used diagnostic method for detecting active CMV infection, particularly in immunocompromised patients. The methodology involves:
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Collecting peripheral blood samples from patients
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Isolating leukocytes (typically 2 × 10^5 cells)
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Preparing cell slides and performing immunofluorescence staining for pp65
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Quantifying positive cells under fluorescence microscopy
Results are reported as the number of pp65 positive cells per 2 × 10^5 leukocytes . This quantitative approach helps in assessing viral burden and monitoring disease progression.
Clinical validation studies have established that pp65 antigenemia positivity correlates with symptomatic disease. Research indicates that patients with ≥10 positive cells per 2 × 10^5 leukocytes frequently present with clinical manifestations of CMV disease . The assay provides valuable information for monitoring treatment response, as decreasing pp65 counts typically indicate successful antiviral therapy.
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What experimental applications exist for CMV pp65 peptides in research?
CMV pp65 peptides serve multiple research purposes in virology and immunology:
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T-cell response characterization: pp65-derived peptides are essential for evaluating antigen-specific T-cell responses through ELISpot assays, intracellular cytokine staining, and tetramer analyses .
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Vaccine development: As a key immunodominant antigen, pp65 is frequently incorporated into vaccine candidates to enhance cellular immune responses. Its ability to elicit strong T-cell responses makes it a prime candidate for next-generation CMV vaccine research .
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Immunotherapeutic development: pp65 peptides serve as targets for developing adoptive T-cell therapies critical for preventing or treating CMV-related complications in immunocompromised patients, particularly transplant recipients .
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Diagnostic assay development: pp65 peptides enable the development and refinement of diagnostic assays for CMV infection, including both antigenemia assays and antibody detection methods .
Researchers typically employ synthetic peptide pools spanning the entire pp65 protein sequence or focus on known immunodominant epitopes depending on the specific research application.
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How does pp65 modulate the host immune response during CMV infection?
CMV pp65 employs sophisticated mechanisms to evade and modulate host immunity:
The protein actively dampens the virion-mediated interferon-like response after viral entry into host cells . Functional genomics research has demonstrated that pp65 specifically targets the IRF-3 signaling pathway, subverting activation of this transcription factor during early infection .
Microarray analysis comparing wild-type virus to pp65 mutant virus has revealed that pp65 modulates host cell transcript levels very early after infection (1-4 hours post-infection) . This modulation affects genes involved in the interferon response pathway, reducing the efficiency of the host's immediate antiviral state.
The immunomodulatory function occurs before viral gene expression begins, indicating that pp65 delivered by the virion immediately acts on host cell signaling pathways . This mechanism represents a sophisticated immune evasion strategy that allows the virus to establish infection before the host can mount effective antiviral responses.
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What is the clinical significance of pp65 antigenemia in transplant recipients?
pp65 antigenemia has established clinical relevance in transplant settings:
Research demonstrates a significant correlation between high pp65 antigenemia values and symptomatic CMV disease. Studies indicate that transplant recipients with higher counts of pp65-positive cells are more likely to develop clinical symptoms .
In kidney transplant recipients, pp65 antigenemia monitoring provides:
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Early detection of CMV reactivation
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Prediction of disease development
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Guidance for preemptive therapy
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Assessment of treatment response
Clinical data from 33 renal transplant recipients with symptomatic CMV disease showed that 32 had detectable pp65 antigenemia . These patients demonstrated clinical improvement after valganciclovir treatment, with decreasing pp65 positive cell counts corresponding to clinical recovery .
Beyond kidney transplantation, pp65 antigenemia has shown utility in patients with systemic lupus erythematosus (SLE), where positivity was found in 36.8% of patients with suspected unclear infection. Those with positive pp65 results commonly presented with lymphopenia, anemia, and higher disease activity scores (SLEDAI) .
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Product Science Overview
Human Cytomegalovirus (HCMV), a member of the herpesvirus family, is a significant pathogen that can cause severe disease in immunocompromised individuals, such as transplant recipients and individuals with HIV/AIDS. One of the key proteins involved in the immune response to HCMV is the phosphoprotein 65 (pp65), encoded by the UL83 gene. This protein is a major component of the viral tegument and plays a crucial role in modulating the host immune response.
The pp65 protein is a 65 kDa phosphoprotein that is abundantly expressed during the late phase of the HCMV replication cycle. It is involved in the assembly and release of the virus and is a major constituent of the dense bodies, which are non-infectious particles produced during HCMV infection . The protein contains immunodominant regions that are recognized by the immune system, making it a key target for immune responses.
Recombinant pp65 is typically produced using Escherichia coli (E. coli) expression systems. The recombinant protein contains the immunodominant regions of pp65, specifically amino acids 297-510, and is often fused to a glutathione S-transferase (GST) tag to facilitate purification . The recombinant pp65 protein is used extensively in research and diagnostic applications, including enzyme-linked immunosorbent assays (ELISA) and Western blots, due to its high immunoreactivity and minimal specificity problems .
The preparation of recombinant pp65 involves cloning the UL83 gene into an expression vector, which is then introduced into E. coli cells. The bacteria are cultured, and the expression of the recombinant protein is induced. The protein is then purified using chromatographic techniques, often involving the GST tag for affinity purification . The purified protein is then used in various applications to study the immune response to HCMV and to develop diagnostic assays.
The pp65 protein plays a significant role in modulating the host immune response. It has been shown to prevent the activation of interferon response factor 3 (IRF-3), thereby inhibiting the interferon response, which is a crucial part of the antiviral defense mechanism . This ability to modulate the immune response makes pp65 a key target for studying the interactions between HCMV and the host immune system.
Recombinant pp65 is widely used in research to study the immune response to HCMV. It is also used in the development of vaccines and diagnostic assays. The protein’s ability to elicit strong immune responses makes it a valuable tool for understanding HCMV pathogenesis and for developing strategies to prevent and treat HCMV infections .
