Virus-induced Changes in the Host

Virus-induced Changes in the Host

Acknowledgement of Country

  • University acknowledges traditional custodians: Pambalong clan of the Awabakal people.

  • Respects Elders past and present, extends respect to all Aboriginal and Torres Strait Islander attendees.

Learning Objectives

  • Understand how viruses affect cells and interact with the host immune system.

  • Describe virus-induced changes leading to disease pathology.

Overview of Virus-Cell Interactions

  • Viruses affect host cells in diverse ways, impacting:

    • Host anti-viral immune response

    • Immunopathology

    • Virus-induced cell/tissue damage

    • Symptoms and disease development

    • Treatment approaches and requirements

Cytopathic Effects (CPE)

  • Direct Cell Killing

    • Some viruses kill host cells during lytic replication (e.g., Enterovirus, Herpesvirus).

    • CPE refers to observable changes caused by virus infection.

  • Inclusion Bodies

    • Characteristic morphological changes during viral infections.

    • Varying characteristics: large/small, intra-nuclear/cytoplasmic.

    • May involve aggregation of viral proteins/nucleic acid within host cells.

Cellular Mechanisms of Damage

  • Shutdown of Host Processes

    • Shutdown of protein synthesis due to viral competition for ribosomes.

    • Degradation of host DNA and inhibition of mRNA transport.

    • Toxic effects from viral proteins.

  • Non-cytocidal Infections

    • Many viruses cause minimal damage to support immune evasion.

    • Infected cells may lose specialized functions (e.g., down regulation of MHC).

  • Viral Oncogenesis

    • Some viruses can transform cells, leading to cancer through mutations or altered gene expression.

    • Example: HPV associated with cervical cancer.

Human Viruses Associated with Cancer

  • Human Papilloma Virus (HPV)

    • Types 6, 11, 16, 18 linked to cervical cancer; Gardasil vaccine developed.

  • Human Immunodeficiency Virus (HIV)

    • Activates oncogenes and suppresses immune response, facilitating co-infection.

  • Hepatitis Viruses

    • Chronic infections can convert into malignancies like Hepatocellular carcinoma.

Immune Responses to Virus Infection

  • Types of Immune Responses

    • Humoral response involves B-cells producing antibodies.

    • Cell-mediated response involves T-cells killing infected cells.

  • Innate Immunity

    • Immediate response to pathogens, does not create memory, may cause tissue damage.

  • Adaptive Immunity

    • Activated by innate immunity, creates long-term memory and improved response to re-exposure.

Immune System Overview

  • Divided into two main systems:

    • Innate immunity (immediate response)

    • Adaptive immunity (develops over days/weeks, creates memory).

Antigen Presentation

  • Activation of adaptive immunity occurs when innate responses fail.

    • Professional Antigen Presenting Cells (APC) internalize and present antigens to T-cells via MHC molecules.

Summary of Key Immune Mechanisms

  • B Cell Activation

    • Requires binding of antigens and helper T-cell support for proliferation and differentiation.

  • Antibody Isotype Switching

    • Determines the antibody class (e.g., IgM, IgG) through signals from cytokines.

  • Plasma B Cells

    • Produce antibodies; some become long-lived memory cells in bone marrow to provide long-term immunity.

Conclusion

  • Understanding virus-induced changes in host cells can inform treatment strategies and enhance immunological control over viral infections, leading to better health outcomes in viral diseases.

Learning Objectives

1. Understand how viruses affect cells?

Viruses affect host cells in diverse ways, impacting:

  • Host anti-viral immune response

  • Immunopathology

  • Virus-induced cell/tissue damage

  • Symptoms and disease development

  • Treatment approaches and requirements

  • Direct Cell Killing: Some viruses kill host cells during lytic replication (e.g., Enterovirus, Herpesvirus). CPE refers to observable changes caused by virus infection.

  • Inclusion Bodies: Characteristic morphological changes during viral infections. Varying characteristics: large/small, intra-nuclear/cytoplasmic. May involve aggregation of viral proteins/nucleic acid within host cells.

  • Shutdown of Host Processes: Shutdown of protein synthesis, degradation of host DNA, and inhibition of mRNA transport due to viral competition for ribosomes. Toxic effects may arise from viral proteins.

  • Non-cytocidal Infections: Many viruses cause minimal damage to support immune evasion. Infected cells may lose specialized functions (e.g., down regulation of MHC).

  • Viral Oncogenesis: Some viruses can transform cells, leading to cancer through mutations or altered gene expression. Example: HPV associated with cervical cancer.

2. Understand how viruses interact with/stimulate the host immune system?

  • Types of Immune Responses

    • Humoral response involves B-cells producing antibodies.

    • Cell-mediated response involves T-cells killing infected cells.

  • Innate Immunity

    • Immediate response to pathogens, does not create memory, may cause tissue damage.

  • Adaptive Immunity

    • Activated by innate immunity, creates long-term memory and improved response to re-exposure.

3. Describe how virus-induce changes can result in disease pathology?

Virus-induced changes can significantly contribute to disease pathology through various mechanisms including:

  • Direct Cell Killing: Many viruses, such as Enterovirus and Herpesvirus, kill host cells during lytic replication, leading to tissue damage and dysfunction. This direct cytopathic effect (CPE) manifests as observable changes in infected cells and tissues.

  • Inclusion Bodies Formation: Viral infections often result in the formation of inclusion bodies, which are characteristic morphological changes within cells. These may involve the aggregation of viral proteins and nucleic acids, impacting cellular function and contributing to pathology.

  • Shutdown of Host Cellular Processes: Viruses can induce the shutdown of essential host cellular processes, such as protein synthesis and mRNA transport, to favor viral replication. This degradation of host DNA and interference with normal cellular functions can lead to cell death or dysfunction, causing disease symptoms.

  • Non-cytocidal Infections: Some viruses employ strategies that cause minimal damage to infected cells to evade the immune response. These infections may lead to the down-regulation of critical functions like Major Histocompatibility Complex (MHC) expression, allowing viruses to persist in the host and prolong illness.

  • Viral Oncogenesis: Certain viruses can induce cancerous changes in host cells through mechanisms like mutations or altered gene expression. For instance, Human Papillomavirus (HPV) is known for its association with cervical cancer, illustrating how viruses can lead to significant long-term pathological consequences.