Immunology Overview Quiz

Lymphatic and Immune System Overview

• The lecture covers the lymphatic and immune systems, including their functions, structures, and distinctions between innate and adaptive immunity.
• Learning objectives include understanding the role of these systems in overall physiology, lymph's source and function, the anatomy of lymph nodes and spleen, and the thymus. Distinctions between innate and adaptive immune responses will also be discussed.
• The human body is divided into physiological systems to allow for study, understanding, identification, prediction, prevention, and problem-solving.

Background

• Immunology focuses on the body's defenses against infections, including how it defends itself, eliminates threats, and develops long-term immunity.
• In 1908, the Nobel Prize was awarded to Paul Ehrlich and Ilya Mechnikov for their contributions to immunology, particularly in understanding immunity and describing phagocytosis respectively.
• The immune system plays a crucial role in maintaining homeostasis in various circumstances.

Lymphatic System Components

• The lymphatic system consists of lymphatic vessels, lymph nodes, and lymph fluid.
• Immune cells and lymphoid organs are also components of the immune system.

Lymph Vessels

• Lymph vessels are one-way systems that move lymph toward the heart.
• Collecting vessels have thin walls and contain internal valves to prevent backflow.
• Larger collecting vessels unite to form lymphatic trunks.
• The lymphatic trunks drain into two main ducts, the right lymphatic duct and the thoracic duct.

Lymph Function

• Lymph is the fluid found in lymphatic vessels and contains interstitial fluid, proteins, pathogens, and absorbed fats.
• The lymphatic system is crucial for supporting the body's defense mechanisms.

Immune System Components

• Immune cells, including macrophages, dendritic cells, neutrophils, granulocytes, lymphocytes (T cells, B cells, and Natural Killer cells).
• Lymphoid organs, including primary lymphoid organs (thymus and bone marrow) and secondary lymphoid organs (lymph nodes, spleen, tonsils, and Peyer's patches).

Thymus Structure and Function

• The thymus is vital for T-cell maturation.
• T-cells become immunocompetent to battle foreign invaders in the thymus.
• Histological features include a capsule, cortex (immature T-cells), and medulla (mature T-cells).

Lymph Node Structure and Function

• Lymph nodes are clustered along lymphatic vessels, particularly in areas like the inguinal, axillary, and cervical regions.
• Lymph nodes help filter lymph, interacting with immune cells and phagocytosing microorganisms.
• • Key features include a capsule, cortex (germinal centers), and medulla (macrophages).
• Lymph enters these nodes through afferent vessels and exits through efferent vessels.

Spleen Structure and Function

• The spleen is located on the left side of the abdominal cavity, behind the diaphragm.
• It promotes lymphocyte proliferation and filters blood.
• Histological features include a capsule, red pulp (macrophages, red blood cell filtration), and white pulp (lymphocytes).

The Main Role of the Immune System

• The immune system distinguishes between "self" and "non-self" (harmful) cells.
• Immune cells recognize antigens via receptors and respond to these signals.

Antigens and Antibodies

• Antigens are molecules that trigger an immune response.
• Antibodies are proteins produced by the immune system targeting specific antigens.
• Receptors are on cell surfaces and only bind to specific ligands.
• Ligands are portions of a molecule that combine with a receptor.

Origin of Immune Cells

• Immune cells are categorized by location (circulating and tissue-resident).
• Circulating immune cells primarily originate in bone marrow.
• Tissue-resident immune cells develop from precursor cells in the yolk sac or fetal liver during embryonic development.

Pathogens

• Pathogens are microorganisms capable of causing diseases.
• Types of pathogens include viruses, bacteria, fungi, and parasites.
• Microbiomes are the micro-environment of commensal microorganisms commonly beneficial to the body.

Activation of Immunity

• Immunity is activated via two broad types of responses to various threats: innate and adaptive.
• Innate immunity is fast and non-specific, while adaptive immunity is slow but specific.

Innate Immune Response Principles

• Macrophages, dendritic cells, and neutrophils play major roles in innate immunity.
• Macrophages are long-lived cells specialized in phagocytosis and are crucial in activating subsequent adaptive responses.
• Granulocytes are short-lived cells primarily involved in phagocytosis.
• Dendritic cells are crucial for activating T-cells.

Innate Recognition and Effects

• Immune cells express receptors that identify and respond to pathogens.
• These receptors, PRRs, recognize pathogen-associated molecular patterns (PAMPs).
• Activated PRRs induce effector functions enabling immune cells to eliminate pathogens directly.
• Inflammation recruits more immune cells and enhances the immune response.

Antigen Presenting Cells (APCs)

• APCs bridge innate and adaptive immune responses.
• These cells include macrophages, dendritic cells, and T cells, which capture antigens from the environment, process them, and present them to other immune cells.
• Extracellular and intracellular antigen processing occurs through different pathways (MHC II and MHC I, respectively) to activate the appropriate cells.

Major Histocompatibility Complex (MHC)

• MHC proteins are crucial for antigen presentation to immune cells.
• MHC I proteins present intracellular antigens to cytotoxic T cells.
• MHC II proteins present extracellular antigens to helper T cells to activate B-cell response.

Other Effector Mechanisms of Immunity

• The immune system can eliminate pathogens through various mechanisms beyond antibodies.
• Cell-mediated immunity involves the activity of cells directly killing pathogens, including CD8 T-cells and NK-cells.
• Cytokines communicate within the immune system to recruit other immune cells, activating immune functions, and/or enhancing the response.
• Complement activation enhances the elimination of pathogens through a cascade of protein activation.

Consequences of Immune Activation

• The outcome and consequences of immune activation vary depending on whether the response involves antibodies or other cell-mediated effector mechanisms.
• Antibodies have specific functions that neutralize pathogens or mark them for destruction.

The Role of Antibodies in Host Defenses

• Antibodies act to neutralize pathogens and toxins through several mechanisms including through neutralization, opsonization, and complement activation.