LO5

Lymphatic System and Immunity: Comprehensive Study Notes

1. Components of the Lymphatic System

  • Lymphatic Vessels:

    • An elaborate network that drains excess protein-containing interstitial fluid.

    • Functions to return the fluid to the bloodstream.

  • Lymph (Fluid):

    • Defined as interstitial fluid once it enters the lymphatic vessels.

  • Lymph Nodes:

    • Monitors lymph for foreign materials.

    • Filtration:

    • Macrophages destroy microorganisms and debris.

    • Immune System Activation:

    • Monitors for antigens and mounts an attack against them.

2. Significance of Lacteals

  • Lacteals are specialized lymphatic vessels found in the small intestine.

  • Their significance lies in their ability to absorb dietary fats and fat-soluble vitamins from the small intestine.

  • They transport these absorbed nutrients through the lymphatic system to the bloodstream.

3. Lymphocytes and Their Functions

  • Lymphocytes:

    • Main warriors of the immune system.

  • Two Main Types:

    • B Cells:

    • Produce antibodies that help in neutralizing pathogens.

    • oversee hummeral immunity

    • T Cells:

    • Protect the body against antigens by directly destroying infected or abnormal cells.


4. Functions of Lymphatic Tissue

  • Primay lymphatic strucutre:

    • Manufacture lymphocytes (both B cells and T cells).

  • Secondary lymphatic structure:

    • Filter:

      • Traps bacteria, viruses, and debris to protect the body.

    • Protect:

      • Initiates immune responses, aiding in the fight against infections.

5. Definitions of Lymphedema and Lymphoma

  • Lymphedema:

    • A condition characterized by swelling due to a buildup of lymph fluid caused by blocked or damaged lymphatic vessels.

  • Hodgkin's Lymphoma:

    • Symptoms include swollen, non-painful lymph nodes, fatigue, fever, and night sweats.

    • Characterized by the presence of Reed-Sternberg cells.

    • Treatment includes chemotherapy and radiation, with a high cure rate.

  • Non-Hodgkin's Lymphoma:

    • Encompasses all lymphoid tissue cancers except Hodgkin's lymphoma.

    • Symptoms include swelling of lymph nodes and spleen, with a more rapidly progressing nature.

    • Lacks Reed-Sternberg cells and often resists chemotherapy, posing a higher fatality risk.

6. Functions of the Spleen

  • Stores breakdown products of RBS for later reuse.

  • Acts as the site for fetal erythrocyte production (which typically ceases after birth).

  • Stores blood platelets.

  • Functions as a site of lymphocyte proliferation.

7. The Thymus vs. Other Lymphoid Tissues

  • The Thymus is a primary lymphoid organ where T cells mature and undergo selection without exposure to antigens.

  • Other lymphoid tissues primarily filter fluids and initiate immune responses.

8. Pathogens

  • Pathogen:

    • Defined as a disease-causing organism.

9. Comparison of Adaptive and Innate Immunity

  • Innate Immunity:

    • Speed: Immediate

    • Specificity: Nonspecific

    • Memory: No

    • Line of Defense: First

    • Main Cells: Macrophages and Natural Killer (NK) cells

    • Main Weapons: Inflammation, complement proteins

  • Adaptive Immunity:

    • Speed: Delayed

    • Specificity: Specific

    • Memory: Yes

    • Line of Defense: Second

    • Main Cells: T cells and B cells

    • Main Weapons: Antibodies and Cytotoxic killing

10. Mechanism of Action of Phagocytes

  • Phagocytes engulf and destroy pathogens through a process involving:

    • Recognition of pathogens.

    • Engulfment via invagination of the plasma membrane.

    • Formation of phagosomes that fuse with lysosomes containing digestive enzymes.

    • Degradation of the engulfed material.

11. First and Second Lines of Defense

  • Innate (Nonspecific) Response:

    • First Line of Defense: Skin + mucous membranes that prevent entry of microorganisms.

      • keep pathogen out

    • Second Line of Defense: Antimicrobial proteins, phagocytes, and various other cells that respond to pathogens after they breach the first line (NK cells, fever)

      • kill pathogen that got in

12. Role of Natural Killer Cells

  • A distinct group of lymphocytes that can lyse (break down) and kill cancer and virus-infected cells.

  • They kill by releasing perforins, which create pores in the target cell membrane, leading to cell death.

13. Flowchart of Inflammation Events

Injury triggers chemical release (histamine + cytokines) → vasodilation (increase permeability) → WBC recruitment (neutrophils + macrophages) → phagocytosis → tissue repair/healing

14. Interferons and Antiviral Use

  • Interferons (IFN):

    • Antiviral proteins released by virus-infected cells.

    • Functions: inhibit viral replication in neighboring cells + activate immune cells such as macrophages and NK cells.

15. Fever: Causes, Benefits, and Risks

  • Cause of Fever:

    • Result of the hypothalamus raising the body temp set point in response to infection or inflammation.

  • Benefits:

    • Inhibits reproduction of bacteria and viruses.

    • Promotes interferon activity.

    • Enhances migration of additional immune cells from blood vessels to tissues.

    • A low fever is generally recommended to be left untreated.

  • Risks of High Fever:

    • High fever is potentially dangerous, especially over 103°F in children and slightly lower thresholds in adults.

    • Can lead to changes in metabolic pathways and denaturation of proteins.

    • Possible seizures and irreversible brain damage can occur if temperature exceeds 106°F.

    • Death is likely if the body temperature exceeds 109°F.

16. Cell-Mediated Immunity vs. Antibody-Mediated Immunity

  • Cell-Mediated Immunity (T Cells):

    • Utilizes T lymphocytes (CD4 and CD8).

    • Directly kills infected or abnormal cells.

    • Does not involve antibodies.

    • Best suited for intracellular pathogens (viruses).

  • Antibody-Mediated Immunity:

    • Involves B cells that produce antibodies.

    • Antibodies bind to pathogens in blood/lymph, neutralizing or tagging microbes for destruction.

    • Most effective against extracellular pathogens.

17. Antigens

  • Antigens:

    • Anything that provokes an immune response, including:

      • Bacteria, toxins, viruses, and other foreign substances.

18. Complete vs. Incomplete Antigens

  • Complete Antigens:

    • Include foreign proteins, nucleic acids, some lipids, and large polysaccharides.

  • Incomplete Antigens:

    • Not immunogenic but are reactive when attached to protein carriers, known as haptens.

20. Differences Between MHC Class I and MHC Class II in Antigen Presentation

  • Class I MHC Proteins:

    • Found on virtually all body cells, specifically on all nucleated body cells.

    • Present intracellular antigens and activate CD8 cytotoxic T cells, leading to the killing of infected cells.

  • Class II MHC Proteins:

    • Found on professional antigen-presenting cells (APCs) such as dendritic cells, macrophages, and B cells.

    • Present extracellular antigens and activate CD4 helper T cells, leading to the coordination of the immune response by aiding B cells (antibody production) and macrophages.

21. Fate of Lymphocytes in Red Bone Marrow

  • In red bone marrow:

    • B cells mature and remain there.

    • T cells leave the marrow while still immature and migrate to the thymus to complete their maturation.

22. Functions of Antigen Presenting Cells (APCs)

  • APCs:

    • Function to phagocytose antigens, process them, and present fragments on MHC molecules.

    • This is crucial for the activation of T cells and initiation of adaptive immunity.

23. Active Humoral Immunity

  • Achieved when B cells encounter antigens and produce antibodies against them.

  • Acquired in two ways:

    • Naturally Acquired:

    • Infection by bacteria or viruses, resulting in the body making its own antibodies.

    • Artificially Acquired:

    • Involves receiving a vaccine, exposing the body to weakened or dead pathogens, prompting the body to produce antibodies.

24. Five Classes of Immunoglobulins

  • IgD:

    • Attached to the surface of B cells and important for B cell activation.

  • IgM:

    • Released during the primary immune response, marking the initial defense against pathogens.

  • IgG:

    • The most abundant immunoglobulin; crosses the placenta to confer passive immunity to the fetus.

  • IgA:

    • Helps prevent the attachment of pathogens to epithelial cell surfaces, playing a key role in mucosal immunity.

  • IgE:

    • Binds to mast cells and basophils, causing the release of histamine when activated, important in allergic reactions and defense against parasites.

25. Functions of CD4 and CD8 Cells

  • CD4 Cells (Helper T Cells, Th):

    • Recognize antigens on MHC II and coordinate/activate the immune response.

    • Activate B cells (leading to antibody production), activate macrophages (enhancing phagocytosis), and assist cytotoxic T cells.

    • Essential for helping other immune cells function effectively.

  • CD8 T Cells (Cytotoxic T Cells, Tc):

    • Recognize antigens on MHC I and directly kill infected or abnormal cells.

    • Release perforins and granzymes that induce apoptosis in target cells.

    • Target mainly virus-infected cells, tumor cells, and transplanted cells.

26. Importance of CD Markers

  • CD Markers:

    • Cell-surface proteins that serve to identify and differentiate various immune cell types, aiding in understanding their roles in the immune response.

27. Functions of Various T Cells

  • Helper T Cells (CD4):

    • Activate B cells, macrophages, and cytotoxic T cells, coordinating the overall immune response.

  • Cytotoxic T Cells (CD8):

    • Kill infected or cancerous cells directly, playing a crucial role in cell-mediated immunity.

  • Regulatory T Cells (Treg):

    • Suppress or slow down the ` response, maintaining homeostasis and preventing autoimmunity.

  • Memory T Cells:

    • Provide faster and stronger long-term protection upon re-exposure to a previously encountered antigen.

28. Autoimmune Disorders

  • Autoimmune Disorder:

    • Occurs when the immune system fails to recognize self-antigens and mistakenly attacks healthy body cells, leading to tissue damage and inflammation.

29. Human Immunodeficiency Virus (HIV)

  • HIV:

    • A retrovirus that targets and attacks the immune system, specifically infecting CD4 helper T cells.

  • Mechanism of Damage:

    • The virus enters CD4 cells, replicates, and eventually destroys them, leading to a gradual loss of helper T cells.

    • can progress to AIDS2