BSCI 20021: Basic Microbiology - Innate Immunity Notes

BSCI 20021: Basic Microbiology - Innate Immunity

Innate Immune System

  • The innate immune system has two forms of defenses:
    • Cellular Defenses
    • Actions of blood and tissue cells that are part of the innate immune system.
    • Molecular Defenses
    • Actions of proteins and small molecules made by a wide variety of cells in the body.

Cellular Defenses

  • Key components of the innate immune system include:

    • Neutrophils
    • A type of granulocyte.
    • Eosinophils
    • A type of granulocyte.
    • Basophils
    • A type of granulocyte.
    • Macrophages
    • Differentiate from monocytes; important for phagocytosis.
    • Monocytes
    • Precursor to macrophages.
    • Lymphocytes
    • Include adaptive immunity cells such as B-cells and T-cells.
    • Dendritic Cells
    • Aid in presenting antigens to T cells.

  • Classification of Leukocytes (White Blood Cells):

    • Granulocytes
    • Neutrophils, eosinophils, basophils.
    • Agranulocytes
    • Includes monocytes and lymphocytes.

  • The distinction between innate and adaptive immunity is nuanced with overlap between the two systems. Innate immunity is characterized by its non-specific nature and lack of memory.

Immune Cell Functions

  • Degranulation:

    • Release of a mixture of molecules that initiate and amplify inflammation:
    • Involves granulocytes such as basophils and mast cells in tissues; these cells release mediators that start the inflammatory process.

  • Phagocytic Activity:

    • Phagocyte movement towards pathogens is termed chemotaxis.
    • Phagocytosis: Process by which phagocytes engulf and digest pathogens.
    • Important phagocytic cells include neutrophils and macrophages.

Step-by-Step of Innate Immune Response

  • Injury:

    • Triggered by skin or tissue damage due to trauma or infectious agents.

  • Inflammation:

    • Vascular Changes:
    • Chemical alarm signals are released by damaged cells and leukocytes; they increase blood flow and vessel permeability.
    • Leukocyte Recruitment:
    • Cytokines recruit leukocytes, starting with neutrophils, followed by monocytes which transform into macrophages; these cells phagocytize invaders and attract more immune cells.
    • Resolution:
    • Inflammation signals decrease as tissue repair begins.
    • Inflammation operates as a chemical alarm system for immune cells, prompting physiological changes which facilitate immune activity at the damage site.

  • Molecular Mechanisms of Inflammation:

    • Vasoactive molecules released that enhance blood flow and permeability by allowing fluids to exit the blood and enter tissue.
    • Major vasoactive substances include:
    • Kinins: Attract leukocytes, aiding in their entry into damaged tissue.
    • Prostaglandins: Amplify the effects of vasoactive molecules and are responsible for causing fever (scientifically termed pyrexia) and increasing pain signals.
    • Histamine: Released by mast cells; contributes to inflammation by causing blood vessel dilation and increased permeability.

  • Cardinal Signs of Inflammation:

    • Redness: Caused by increased blood flow.
    • Heat: Due to elevated blood perfusion.
    • Swelling: Resulting from fluid influx into tissues.
    • Loss of function: Area may not function normally due to damage or pain.
    • Pain Signals: Result from tissue injury and chemical mediators (e.g., bradykinin).

Phagocytosis Stages

  • Phagocytoic cells, such as neutrophils and macrophages, attach to microbes using receptors and engulf them by endocytosis.
  • Upon ingestion, microbes are enclosed in a vesicle that fuses with lysosomes containing digestive enzymes that destroy the microbes.
  • This process allows for the recycling of microbial proteins, which can signal and activate other immune cells, thus linking innate immunity with adaptive immune responses.

Study Guide Highlights

  • Understand the concept of inflammation and its triggers.
  • Familiarize with the major steps/stages of inflammation and the processes involved in each stage.
  • Recognize the key vasoactive molecules and how they induce vascular changes during inflammation.
  • Memorize the five cardinal signs of inflammation and comprehend how vascular changes manifest those signs.
  • Learn the stages of phagocytosis, comprehending how pathogens are detected, engulfed, and processed by immune cells.