Immune cells | Introduction

Overview of the Immune System

• Immune cells are categorized into two functional groups:

  • Innate Immune Response

  • Adaptive Immune Response

Innate Immune Response

• Definition: First line of defense against pathogens, always present in the body.

• Characteristics:

  • Response is the same regardless of the type of invader.

  • An evolutionarily older defense mechanism.

Adaptive Immune Response

• Definition: Specialized, more recently evolved defensive mechanism against specific pathogens.

• Characteristics:

  • Response varies based on the type of invader.

Functions of Immune Cells

• Main functions include:

  • Phagocytosis: Engulfing and digesting foreign materials.

  • Swallowing Foreign Substances: Eliminating dangerous entities.

  • Inflammation: Reacting to pathogens and injuries.

  • Modulating Immune Responses: Regulating activity within the immune system.

  • Antigen Presentation: Displaying foreign antigens to trigger immune responses.

  • Cell Killing: Targeting infected or dysfunctional cells.

  • Producing Antibodies: Generating proteins that recognize specific pathogens.

Diagram Breakdown

• Bone Structure:

  • Immune cells originate around the bone in blood vessels.

• Extracellular Tissue: Indicates surrounding tissue where immune cells operate.

• Lymphoid Tissue: Includes secondary tissues, like spleen and lymph nodes.

Immune Cell Origin

• Embryonic Development: Cells arise from the yolk sac or liver.

• Postnatal Development: All immune cells are produced in the bone marrow.

• Key Structure:

  • Hemopoietic Stem Cell: The primary source of all immune cells.

Myeloid Lineage (Innate Cells)

• Cells predominantly involved in the innate immune response:

  • Phagocytes:

    • Neutrophils: Most abundant; important in inflammation and injury.

    • Eosinophils: Important for dealing with parasites.

    • Macrophages:

      • Derived from monocytes, effective in phagocytosis.

      • Differentiate into specialized macrophages in tissues (e.g., alveolar macrophages in lungs).

      • Serve as antigen-presenting cells.

  • Mast Cells:

    • Contain granules (histamines, heparin) for initiating inflammation.

    • Located in connective tissues, contributing to allergic reactions.

  • Megakaryocytes:

    • Break down into platelets, involved in clotting and inflammation.

  • Polymorphonuclear Granulocytes (PMN):

    • Cells that appear to have multiple nuclei, including neutrophils, eosinophils, and basophils.

Lymphoid Lineage (Adaptive Cells)

• Involves cells associated with adaptive immunity:

  • Natural Killer (NK) Cells:

    • Kill infected or dysfunctional cells; part of innate response.

  • B and T Lymphocytes:

    • B Cells: Mature in bone marrow; produce antibodies.

    • T Cells: Mature in thymus; involved in cell-mediated responses.

      • Includes helper T cells and cytotoxic T cells.

    • Both cell types migrate to secondary lymphoid tissues for final differentiation.

  • Dendritic Cells:

    • Can originate from both lineages; function in antigen presentation to T cells.

Summary of Immune Cells

• Myeloid Line: Primarily involved in innate response with roles in phagocytosis, inflammation, and initial defense.

• Lymphoid Line: Primarily involved in adaptive response, specializing in antibody production and targeted immune responses.

• Both categories work cohesively to execute functions like phagocytosis, inflammation, killing infected cells, and generating immune memory.

Next Steps

• Future videos will delve deeper into each subtype of immune cells.

Overview of the Immune System

The immune system is a complex network of cells, tissues, and organs that work together to defend the body against harmful invaders such as pathogens (bacteria, viruses, fungi, and parasites) and to maintain homeostasis. Immune cells are categorized into two primary functional groups:

Innate Immune Response

Definition:

The innate immune response serves as the first line of defense against pathogens, functioning continuously throughout the body to provide immediate, non-specific protection.

Characteristics:

• Immediate Response: It acts within minutes to hours after exposure to pathogens without the need for prior exposure.

• Non-specific Defense: The response is uniform regardless of the type of invader, targeting a broad range of pathogens.

• Evolutionarily Older Mechanism: This system has existed longer in evolutionary terms and is equipped to handle common infections.

Adaptive Immune Response

Definition:

The adaptive immune response is a specialized, more recently evolved defense mechanism that targets specific pathogens and adapts its response based on the nature of the invader.

Characteristics:

• Varied Response: Responses can be tailored uniquely to each pathogen, providing a more effective defense following initial exposure.

• Memory Formation: This system remembers past infections, allowing for a quicker and more robust response upon re-exposure to the same pathogen.

Functions of Immune Cells

The primary functions of immune cells include:

• Phagocytosis: Immune cells like macrophages and neutrophils engulf and digest foreign materials, removing pathogens and debris from the body.

• Elimination of Foreign Substances: Different immune cells are specialized to neutralize various harmful entities.

• Inflammation: A protective response that enhances blood flow and immune cell access to sites of infection or injury, characterized by redness, heat, swelling, and pain.

• Modulating Immune Responses: Balancing the immune response to effectively combat pathogens while preventing excessive damage to host tissues.

• Antigen Presentation: Critical for activating T cells, antigen-presenting cells (APCs) display foreign antigens on their surface, initiating targeted immune responses.

• Cell Killing: Certain immune cells are directly involved in targeting and destroying infected or malfunctioning cells in the body.

• Producing Antibodies: B cells generate specific antibodies that bind to pathogens, marking them for destruction or neutralization.

Diagram Breakdown

Bone Structure:

• Immune Cell Origins: Immune cells are produced around bones in blood vessels, where they first enter circulation.

• Extracellular Tissue: Immune cells patrol surrounding tissues to monitor for signs of infection or injury.

• Lymphoid Tissue: Secondary lymphoid tissues such as the spleen and lymph nodes provide sites for immune cells to interact and coordinate responses.

Immune Cell Origin

Embryonic Development:

During early development, immune cells arise from the yolk sac or fetal liver, laying the groundwork for the immune system.

Postnatal Development:

All immune cells are produced in the bone marrow post-birth.

Key Structure:

• Hemopoietic Stem Cell: The primary progenitor cell from which all immune cells derive.

Myeloid Lineage (Innate Cells)

Cells predominantly involved in the innate immune response include:

• Phagocytes:

  • Neutrophils: The most abundant white blood cells, instrumental in inflammation and tissue injury response.

  • Eosinophils: Key players in combating multicellular parasites and involved in allergic responses.

  • Macrophages: Derived from monocytes, proficient in phagocytosis, they differentiate into specialized forms in various tissues (e.g., alveolar macrophages in lungs) and function as antigen-presenting cells.

• Mast Cells: Contain granules filled with histamines and heparin; play a role in initiating inflammation and are crucial in allergic reactions, located in connective tissues.

• Megakaryocytes: Large cells that fragment into platelets, essential for blood clotting and mediating inflammation responses.

• Polymorphonuclear Granulocytes (PMN): A group of white blood cells characterized by a lobed nucleus that includes neutrophils, eosinophils, and basophils, all integral to the innate response.

Lymphoid Lineage (Adaptive Cells)

Involves cells associated with adaptive immunity:

• Natural Killer (NK) Cells: Part of the innate response, they are crucial for killing infected or dysfunctional cells without prior sensitization.

• B and T Lymphocytes:

  • B Cells: Mature in the bone marrow and are responsible for antibody production, adapting to recognize specific antigens.

  • T Cells: Mature in the thymus and are involved in cell-mediated immunity; they include helper T cells (which aid in activating other immune cells) and cytotoxic T cells (which kill infected cells). Both lymphocyte types migrate to secondary lymphoid tissues for final differentiation and activation.

• Dendritic Cells: These cells can originate from both lineages and are crucial for capturing and presenting antigens to T cells, bridging innate and adaptive immunity.

Summary of Immune Cells

• Myeloid Line: Primarily involved in the innate immune response, focusing on rapid action such as phagocytosis and inflammation to provide initial defense against pathogens.

• Lymphoid Line: Primarily involved in the adaptive immune response, specializing in antibody production and developing targeted immune responses to eliminate specific threats.

• Cohesive Functioning: Both categories collaborate to execute vital immune functions, including phagocytosis, inflammation, killing infected cells, and generating immune memory for future protection.

Next Steps

Future videos will delve deeper into each subtype of immune cells and their specific roles, as well as current research and advancements in immunology.