Immunology and Lymphatic System Quiz

Lymphatic System

• The lymphatic system is a network of vessels, tissues, and organs that help maintain fluid balance in the body and fight infection.
• It consists of lymph, lymphatic vessels, structures, organs containing lymphatic tissue, and red bone marrow.

Functions of the Lymphatic System

• Drains excess interstitial fluid.
• Transports dietary lipids.
• Carries out immune responses.

Immunity or Resistance

• Ability to ward off damage or disease through our defenses.
• Two types of immunity:
  • Innate or nonspecific immunity – present at birth.
  • Adaptive or specific immunity – specific recognition of invaders with a memory component.
  • innate immunity is no specific to a particular pathogen, adaptive immunity does.

Lymphoid Cells

• Lymphocytes - main cells involved in the immune response.
• Two main varieties:
  • T cells – manage the immune response and attack foreign cells.
  • B cells – produce plasma cells that secrete antibodies to immobilize antigens.
• Other Lymphoid Cells:
  • Macrophages – phagocytize foreign substances and help activate T cells.
  • Dendritic cells – spiny-looking cells similar to macrophages that capture antigens and bring them back to lymph nodes.
  • Reticular cells – fibroblast-like cells that produce stroma and support other cell types in lymphoid organs.

Lymphatic Tissues and Organs

• Two groups based on function:
  • Primary lymphatic organs - sites where stem cells divide and become immunocompetent (to produce a normal immune response):
    • Red bone marrow
    • Thymus
  • Secondary lymphatic organs - sites where most of the immune response occurs:
    • Lymph nodes
    • Spleen
    • Lymphatic nodules

Lymphoid Organs

• Tonsils – located along the pharynx.
• Thymus – located in the thorax, most active during youth.
• Spleen – curves around the left side of the stomach.
• Peyer's patches – located in the intestine.
• Appendix

Thymus

• Internal Anatomy: Thymic lobes contain an outer cortex and inner medulla.
• Cortex contains densely packed lymphocytes and scattered macrophages.
• Medulla contains fewer lymphocytes and thymic (Hassall's) corpuscles.
• The thymus differs from other lymphoid organs as it functions strictly in T lymphocyte maturation and does not directly fight antigens.
• The stroma of the thymus consists of star-shaped epithelial cells.
• Thymocytes secrete hormones to stimulate lymphocytes to become immunocompetent.
• Outer cortex is composed of large numbers of T cells.
• Immature T cells migrate from red bone marrow to proliferate and mature.
• Dendritic cells derived from monocytes help educate T cells.
• Specialized epithelial cells educated T cells through positive selection.
• Only 25% survive this process.
• Macrophages clear out dead cells.
• More mature T cells migrate from the cortex to the medulla.
• More epithelial cells, dendritic cells, and macrophages exist in the medulla.
• Thymus shrinks with age.

Lymph Nodes

• Located along lymphatic vessels, scattered throughout the body.
• Stroma - supporting connective tissue (capsule, trabeculae, reticular fibers, and fibroblasts)
• Parenchyma – functional part:
  • Outer cortex – aggregates of B cells called lymphatic nodules (follicles) – site of plasma cell and memory B cell formation.
  • Inner cortex – mainly T cells and dendritic cells.
  • Medulla - B cells, antibody-producing plasma cells from cortex, and macrophages.

Lymph

• Lymph flows through a node in one direction only, entering through afferent lymphatic vessels and exiting through efferent lymphatic vessels.
• Lymph enters sinuses (irregular channels) into the medulla.
• Lymph nodes function as a filter, destroying substances trapped by macrophages or the immune response of lymphocytes.
• Lymph nodes have two basic functions:
  • Filtration – macrophages destroy microorganisms and debris.
  • Immune system activation – monitoring for antigens and mounting an attack against them.
• Lymph nodes are bean-shaped and surrounded by a fibrous capsule.
• Trabeculae extend inward from the capsule and divide the node into compartments.
• Contain cortex and medulla with specific functions.

Spleen

• Largest single mass of lymphatic tissue in the body.
• Stroma – capsule, trabeculae, reticular fibers, and fibroblasts.
• Parenchyma:
  • White pulp – lymphatic tissue that includes lymphocytes and macrophages with B and T cells capable of carrying out immune responses.
  • Red pulp – blood-filled venous sinuses and splenic cords(Bilroth's) containing red blood cells, macrophages, lymphocytes, plasma cells, and granulocytes that remove ruptured, worn-out, or defective blood cells.
• Storage of up to 1/3 of body's platelet supply and production of blood cells during fetal life.

Lymphatic Nodules

• Not surrounded by a capsule.
• Scattered throughout the lamina propria of mucous membranes (GI, urinary, reproductive tracts).
• Mucosa-associated lymphatic tissue (MALT) of respiratory tract.
• Most are small and solitary.
• Some are larger – tonsils, Peyer’s patches, and appendix.

Adaptive Immunity

• Ability of the body to defend itself against specific invading agents.
• Antigens (Ags) – substances recognized as foreign and provoking an immune response.
• Distinguished from innate immunity by:
  • Specificity
  • Memory

Maturation of T Cells and B cells

• Both develop from pluripotent stem cells originating in red bone marrow.
• B cells complete their development in red bone marrow.
• T cells develop from pre-T cells that migrate from red bone marrow to the thymus.
• Helper T cells (CD4 T cells) and cytotoxic T cells (CD8 T cells).
• Immunocompetence - Ability to carry out adaptive immune response.
  • Have antigen receptors (make protein that is inserted into their plasma membranes) that identify specific antigens.

Types of Adaptive Immunity

• Cell-mediated – Cytotoxic T cells directly attack invading antigens, particularly effective against viruses, fungi, bacteria, some cancer cells and foreign tissues. Involve cells attacking cells.
• Antibody-mediated – B cells transform into plasma cells that make antibodies(Abs). Work against extracellular pathogens. Helper T cells aid in both types.

Clonal Selection

• Process by which a lymphocyte proliferates and differentiates causing a specialized cell to respond to a specific antigen.
• Clone - population of identical cells that recognize the same antigen.
• Occurs in secondary lymphoid organs and tissues
• Indicator: swollen lymph nodes and tonsils during sickness.
• Effector cells (inactivation) – active helper T cell, cytotoxic T cell, plasma cell, and they die after immune response.
• Memory cells – do not participate in initial immune response, respond quickly to subsequent invasions and generate effector and memory cells with long life spans. Destroy the ANTG fast.

Antigens

• Antigens have two characteristics:
  • Immunogenicity – ability to provoke an immune response.
  • Reactivity - ability to react with antibodies it provoked.
• Typically, only certain parts of a large antigen molecule trigger a response (epitope).
• Human immune system is able to recognize and bind to at least a billion different epitopes.

Pathways of Antigen Processing

• B cells can recognize and bind to antigens in lymph, interstitial fluid, or blood plasma.
• T cells only recognize fragments of antigens processed and presented in a certain way.
• Antigenic proteins are broken down into peptide fragments and associated with MHC molecules.
• Antigen presentation - antigen-MHC complex inserts into plasma membrane.
• Pathway depends on whether antigen is outside or inside body cells.

Antigen Presenting Cells (APCs)

• Process and present antigens.
• APCs include dendritic cells, macrophages, and B cells.
• Location: Places where antigens like to penetrate (skin: Langerhans cells are dendritic cells; mucous membranes of respiratory, gastro, urinary, and reproductive tracts, lymph nodes).
• APCs migrate from tissues via lymphatic vessels and to lymph nodes.

Exogenous and Endogenous Antigens

• Exogenous - present in fluid outside body cells.
  • APC- include dendritic cells, macrophages, and B cells.
  • Ingest, process, place next to MHC-II molecule in plasma membrane, present to T cells.
• Endogenous - antigens inside body cells.
  • Infected cell displays antigen next to MHC-I.
• After processing, APCs migrate to lymphatic tissues to present antigen to T cells, triggering cell-mediated/antibody-mediated responses.

Cell-mediated Immunity

• Activation of T cells: First signal in activation, T-cell receptors(TCRs), CD4 and CD8 proteins, Second signal required for activation.
• Costimulation- required for virtually all immune responses - important for B, T, and NK cell activation.
• Prevention of harmful immune responses - anergy - recognition without costimulation, prolonged state of inactivity.
• Activation and clonal selection of helper T cells - recognize exogenous antigen fragments with MHC-II, makes active helper T cells and memory helper T cells, helps other adaptive immune responses combat intruders.
• Activation and clonal selection of cytotoxic T cells - Most that display CD8, recognize antigens combined with MHC-I, undergoes clonal selection - needed to attack host cells with intracellular pathogens.

Elimination of Invaders

• Cytotoxic T cells - migrate to seek out and destroy infected target cells, using granzymes to cause apoptosis (fragmentation of cellular contents) or releasing perforin and/or granzymes to cause cytolysis (cell bursting).
• Immunological surveillance - Tumor antigens displayed on cancerous cells are targeted by cytotoxic T cells, macrophages, and natural killer cells.

Antibody-mediated Immunity

• Activation and clonal selection of B cells – During activation, antigen binds to the B-cell receptor (BCR).
• Respond to unprocessed antigens, antigen taken into B cell, combined with MHC-II, moved to plasma membrane, helper T cell binds, delivers costimulation.
• Once activated, B cells undergo clonal selection and plasma cells produce Antibodies that travel to the invasion site.
• Memory B cells – wait for antigen reappearance, do not secrete antibodies.

Antibodies (Ab)

• Combine specifically with epitope of antigen for production.
• Belong to group of glycoproteins called globulins.
• Antibodies are immunoglobulins (Igs).
• Contains 4 polypeptide chains (two heavy, two light chains).
• Variable region: antigen-binding site (bivalent).
• Constant region: identical for each of the five classes – determines the type of reaction.

Immunological Memory

• Thousands of memory cells.
• Exists after initial encounter with an antigen.
• Next time antigen appears, can proliferate and differentiate hours, faster and stronger secondary response.

Self-recognition and self-tolerance

• Your T cells must have:
  • Self-recognition – be able to recognize your own MHC.
  • Self-tolerance – lack reactivity to peptide fragments from your own proteins.
• Pre-T cells in the thymus develop self-recognition via positive selection.
• Cells that cannot recognize your own MHC undergo apoptosis.
• Self-tolerance occurs through negative selection wherein T and B cells that recognize self peptide fragments are eliminated.
• Apoptosis is a way for cells to self-destruct.
• Anergy – Remain alive but unresponsive.

Test your knowledge on the immune system and lymphatic organs with this quiz. You will answer questions about lymphocytes, the functions of various immune cells, and the roles of primary and secondary lymphatic organs. Perfect for students learning about immunology and body systems.