IM 1

Overview of the Immune System

  • The immune system's primary purpose is to prevent pathogens from entering the body.

    • It consists of multiple systems that act as barriers against potential infections.
    • If pathogens penetrate these barriers, the immune system can identify and respond to them.

  • Key aspects of the immune response include:

    • Elimination or neutralization of pathogens.
    • Memory formation for pathogens, aiding in a more robust response during future infections.

Types of Immune Response

  • Two aspects are critical in understanding the immune system:
    1. Innate Immune Response
    • It is present from birth.
    • Represents an immediate, non-specific response to pathogens.
    • Lacks memory capabilities.
    1. Adaptive Immune Response
    • Takes time to develop after exposure to pathogens.
    • Is highly specific for particular pathogens.
    • Can develop memory for enhanced future responses.

Cells Involved in the Immune System

  • Immune system cells are categorized as white blood cells (leukocytes). Key cell types include:

    • Neutrophils:

    • Most abundant white blood cells.

    • Circulate in the bloodstream and exit into tissues via diapedesis.

    • Possess pathogen recognition receptors.

    • Function in innate response through phagocytosis (ingesting and destroying pathogens).

    • Release cytokines and chemokines that call other immune cells.

    • Macrophages:

    • Experts in phagocytosis and removal of dead cells.

    • Release cytokines to stimulate immune cells.

    • Present antigens to lymphocytes for adaptive response enhancement.

    • Dendritic Cells:

    • Located at body surfaces such as skin and gastrointestinal mucosa.

    • Conduct phagocytosis and present antigens to lymphocytes in lymph nodes, crucial for initiating adaptive immune responses.

    • Granulocytes:

    • Notable for prominent granules in their cytoplasm; include:

      • Eosinophils
      • Mast Cells
      • Basophils

    • Play roles in allergic reactions and inflammation through histamine release and pro-inflammatory cytokines.

    • Lymphocytes:

    • Includes several types:

      • Natural Killer Cells (innate immune response):
      • Recognize and kill virus-infected and potentially cancerous cells.
      • B Lymphocytes:
      • Bind to antigens and can present them to T cells.
      • Mature into plasma cells to produce antibodies, contributing to humoral immunity.
      • Have memory cells for future encounters with the same pathogen.
      • T Lymphocytes:
      • Primed by interactions with antigen-presenting cells.
        • T Helper Cells:
        • Assist B lymphocytes and macrophages by secreting cytokines.
        • Cytotoxic T Cells (Killer T Cells):
        • Induce apoptosis in infected cells displaying specific antigens.
      • Have memory cells to enhance response to subsequent infections.

Aspects of Innate Immunity

  • Innate immunity is inherently present and includes:

    • Barrier Surfaces:
    • Epithelial surfaces with tight junctions prevent pathogen entry.
    • Antimicrobial Peptides:
    • Found on skin surfaces to kill pathogens.
    • Commensal Bacteria:
    • Non-harmful bacteria that inhibit pathogen growth.
    • Chemical Defenses:
    • Low pH of gastric acid destroys ingested pathogens.
    • Mucous Membranes trap pathogens, aided by ciliated cells that clear mucus.
    • Tears contain lysozymes that degrade bacterial cell walls.
    • Sebaceous glands also emit substances harmful to bacteria.

  • Complement System:

    • Comprises approximately 13 distinct proteins operating in the plasma.
    • Can be activated through various pathways upon pathogen entry.
    • Functions include:
      • Opsonization: Enhances phagocytosis by marking pathogens for destruction (e.g., through dendritic cells).
      • Formation of the Membrane Attack Complex: Perforates pathogen cell membranes, leading to cell lysis.
      • Enhances inflammation by increasing vascular permeability and blood flow via vasodilation, enabling better leukocyte access to infection sites.