Immune Response to Viruses

Review of the Complement System

  • Definition: The complement system consists of about 20 proteins made in the liver and present in plasma, activated during immune responses.

  • Functions upon activation:

    • Cell lysis: Destruction of pathogens by breaking down their cell membranes.

    • Inflammation: Recruitment and activation of immune cells leads to increased blood flow and immune activity at infection sites.

    • Neutralization: Binding of antibodies to pathogens inhibits their function.

    • Enhanced phagocytosis: Opsonization allows phagocytes to recognize and engulf pathogens more easily.

    • Clearance of immune complexes: The complements help remove antigen-antibody complexes from the bloodstream.

Viral Infection Mechanism

  • Virus Entry: A virus invades a host cell, utilizing the cell's machinery to reproduce.

  • Viral Components: Viral nucleic acids can be either DNA or RNA, which initiate transcription and translation processes in the host.

  • Interferon Production:

    • Host cell (Cell #1) produces interferon prior to cell death due to virus replication.

    • Interferon acts as a signaling molecule, binding to receptors on neighboring cells (Cell #2) to trigger protective responses.

    • Result: Cell #2 produces antiviral proteins that block viral reproduction, thus protecting it.

Inflammatory Response

  • Physiological symptoms: Heat, redness, swelling, and pain are hallmarks of inflammation, which facilitate immune response and signal injury.

  • Key players:

    • Infected Cells: Produce inflammatory mediators and interferons.

    • Natural Killer Cells: Activated by interferons to lyse infected cells.

    • B Cells: Activated by viral particles; they produce antibodies that neutralize the virus.

    • Macrophages: Ingest dead cells and present antigens to helper T cells, activating the adaptive immune response.

Immune Response to Common Cold

  • Initial Infection: Virus infects epithelial cells in the nasal epithelium, triggering an inflammatory response.

  • Ole Cell Death: Infected cells die but release interferon, aiding neighboring cells.

  • Natural Killer Cells Activation: Interferons stimulate natural killer cells which then lyse infected cells.

  • B Cell Activation: Viral particles bind to B cells, prompting antibody production that neutralizes the virus.

  • Macrophage Role: Function as antigen-presenting cells after digesting dead cells, leading to the activation of helper T cells.

  • Helper T Cells: Release cytokines to further activate cytotoxic T cells, which destroy infected cells using perforin.

    • Mechanism of Action: Killer T cells release perforin to create pores in infected cell membranes, facilitating the entry of destructive enzymes.

Summary of Connections

  • Understand the roles of interferons, natural killer cells, B cells, and macrophages in the immune response.

  • Be able to outline the sequence from viral infection of a cell to the overall immune reaction, highlighting how the inflammation, interferons, and antibody production interact.

  • Review diagrams that depict these processes for a comprehensive understanding before moving into discussions of more specific pathogens like COVID-19.