Mar 16

Interferons

  • Definition: Class one interferons (e.g., interferon alpha and beta) which function against viral infections.

  • Not expected to memorize specific types, but understanding their role is important.

  • Mechanism of Action:

    • Viruses infect somatic cells activating gene expression for interferon production.

    • Infected cells release interferons via exocytosis into the surrounding environment.

    • Neighboring uninfected cells detect interferons through receptors leading to production of antiviral proteins capable of:

    • Blocking viral replication.

    • Inhibiting the conversion of viral mRNA to DNA.

  • Significance: Helps prevent the spread of viral infections to neighboring cells, protects against cancer by inhibiting viral replication.

Inflammation

  • Definition: A nonspecific response to tissue injury or microbial invasion.

  • Characteristics:

    • Can be beneficial in small doses but problematic when systemic, causing collateral damage.

  • Trigger: Tissue injury or microbial invasion triggers inflammation.

  • Chemical Mediators: Involved in the inflammatory response (e.g., histamine) which causes:

    • Vasodilation, increasing blood flow.

    • Increased vascular permeability allowing white blood cells and clotting factors to access the area of injury.

Hallmark Symptoms of Inflammation

  • Key Symptoms (Latin terms may be noted by some):

    • Redness (rubor)

    • Swelling (tumor)

    • Heat (calor)

    • Pain (dolor)

    • Potential loss of function.

Localized vs. Systemic Inflammation

  • Localized Inflammation: Confined to one area, exhibits hallmark symptoms, and aids tissue repair and pathogen clearance.

  • Systemic Inflammation:

    • Can occur due to microbes in circulation or large-scale tissue injury (e.g., burns).

    • Affects multiple body areas, leading to potential vascular shock from fluid accumulation outside the bloodstream.

    • Can cause fever due to pyrogen release affecting the hypothalamus, increasing metabolic reactions.

White Blood Cells (Leukocytes)

  • Constitute the second line of defense, playing crucial roles in innate immunity.

  • Neutrophils:

    • Most abundant type.

    • First responders to infection.

    • Engage in phagocytosis and release inflammatory chemicals to recruit more immune cells.

  • Monocytes (Becoming Macrophages):

    • Larger and more efficient phagocytes.

    • Can be fixed in tissues (e.g., Kupffer cells in liver).

    • Produce chemical signals and activate additional immune responses.

  • Basophils/Mast Cells:

    • Not phagocytes but release pro-inflammatory chemicals, primarily histamines.

  • Eosinophils:

    • Secrete extracellular enzymes to combat eukaryotic parasites and modulate inflammatory responses.

  • Natural Killer (NK) Cells:

    • Nonphagocytic lymphocytes that target transformed (cancerous) or infected cells.

Summary of Cells in Innate Immunity

  • White blood cells can be categorized based on their functions and characteristics, contributing to both innate and adaptive immunity once activated.

Adaptive Immunity

  • Involves a specific immune response to pathogens, taking longer to activate than innate responses (10-14 days).

  • Antigen Definition: Foreign substances that elicit an immune response.

    • Naturally occurring antigens stimulate an immune response directly, while haptens require other proteins for recognition.

  • Memory Cells:

    • Formed after initial exposure to antigens, allowing for a quicker future response.

B Cells and T Cells

  • B Cells:

    • Produce antibodies and are responsible for humoral immunity.

    • Differentiate into plasma cells (secreting antibodies) and memory B cells (for future responses).

  • T Cells:

    • Include cytotoxic T cells (destroy infected cells) and helper T cells (activate B and T cells).

      • activated T cells and macrophages release cytokines to mobilize immune cells and attract other leukocytes

    • Regulatory T cells help shut down the immune response after clearance of the pathogen.

    • Hapten: small molecules that, when combined with larger proteins, can elicit an immune response, but are not immunogenic by themselves.

  • Dendritic Cells:

    • Serve as antigen-presenting cells that initiate T and B cell activation.

Importance of Antigenic Determinants

  • Recognized by lymphocytes during an immune response.

  • Multiple determinants enhance immune response robustness.

  • Antigenic variability (epitopes) can complicate vaccine effectiveness due to pathogen mutation.

Mechanism of Lymphocyte Activation

  • When lymphocytes recognize foreign antigens through their receptors, they undergo clonal expansion to effectively combat the infection.

  • MHC Complexes: Important for distinguishing self from non-self antigens, involved in presenting antigens to T cells.

    • Class I MHC: Found on all nucleated cells and present internal cellular proteins.

    • Class II MHC: Found on antigen-presenting cells (APCs) and present external pathogens.

Conclusion

  • The immune system is a complex interplay of various cells and molecules, with innate responses providing rapid defense and adaptive responses offering specificity and memory against pathogens. Understanding these mechanisms is crucial in immunology and for successful application in health sciences.