Chap 16 – BYU – Flashcards
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| Third Line of Defense |
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| • Is called specific or acquired immunity – The body’s ability to recognize and defend itself against distinct invaders and their products – Is a “smart” system whose “memory’ allows it to respond rapidly to a second encounter with a pathogen |
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| Elements of Specific Immunity |
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| • Is acquired over time • Immunologists are scientists who study the cells and chemicals involved in specific immunity • Antigens trigger specific immune responses • Various cells, tissues, and organs are part of specific immunity – Includes B and T lymphocytes |
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| Antigens |
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| • Molecules that trigger a specific immune response • Include components of bacterial cell walls, capsules, pili, and flagella, as well as proteins of viruses, fungi, and protozoa • Food and dust can also contain antigenic particles • Enter the body by various methods: – Through breaks in the skin and mucous membranes – Direct injection, as with a bite or needle – Through ingestion or inhalation |
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| The Nature of Antigens Lymphatic System |
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| • Screens the tissues of the body for foreign antigens • Composed of lymphatic fluid, vessels and lymphatic cells |
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| Lymphatic Vessels |
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| • Form a one-way system that conducts lymph from local tissues and returns it to the circulatory system – Lymph is a liquid with similar composition to blood plasma that arises from fluid leaked from blood vessels into surrounding tissues |
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| Lymph Nodes |
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| • House leukocytes that recognize and attack foreign antigens present in the lymph • Concentrated in the cervical (neck), inguinal (groin), axillary (armpit), and abdominal regions • Receives lymph from afferent lymphatic vessels and drains lymph into efferent lymphatic vessels |
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| Other Lymphoid Tissues and Organs |
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| • Spleen – Similar in structure and function to the lymph nodes – Filters bacteria, viruses, toxins, and other foreign matter from the blood • Tonsils and mucosa-associated lymphoid tissue (MALT) – Physically trap foreign particles and microbes that are ingested or inhaled – MALT includes the appendix, lymphoid tissue of the respiratory tract, and Peyer’s patches in the wall of the small intestine |
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| B Lymphocytes |
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| • Arise and mature in the bone marrow • Found primarily in the Secondary lymphoid tissue: spleen, lymph nodes, bone marrow, and Peyer’s patches • Small percentage of B cells circulate in the blood • Major function is the differentiation into plasma cells which secrete antibody |
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| Antibodies |
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| • Also called immunoglobulins (Ig) • Soluble, glycoprotein molecules that bind antigen • Secreted by plasma cells, which are activated and differentiated B cells • Considered part of the humoral immune response since bodily fluids such as lymph and blood were once called humors |
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| Antibody Function |
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| • Antigen-binding sites are complementary to antigenic determinants (epitopes) – Due to the close fit, can form strong, noncovalent interactions – Hydrogen bonds, ionic attractions, and hydrophobic interactions are involved |
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| Antibody Functions: |
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| • Neutralization (both viruses and toxins) • Opsonization • Agglutination • Activation of complement |
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| Classes of Antibodies |
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| • A single type of antibody is not sufficient for the multiple types of invaders to the body • The class involved in the immune response depends on the type of foreign antigen, the portal of entry, and the antibody function needed • 5 different classes of antibodies |
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| Five Classes of Immunoglobulins B Cell Receptor (BCR) |
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| • Is an antibody that remains associated with the cytoplasmic membrane • Each B lymphocyte has multiple copies of a single type of BCR (either IgM or IgD) • Antigen binding site is identical to that of the secreted antibody for that particular cell • The randomly generated antibody variable region determines the BCR specificity |
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| B Cell Receptor (BCR) |
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| • Each BCR on an individual cell is complementary to only one antigenic determinant |
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| T Lymphocytes |
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| • Produced in the red bone marrow and mature in the thymus • Circulate in the lymph and blood and migrate to secondary lymphoid tissue: lymph nodes, spleen, and Peyer’s patches • Part of the cell-mediated immune response because they act directly against various antigens – Endogenous invaders – Many of the body’s cells that harbor intracellular pathogens – Abnormal body cells such as cancer cells that produce abnormal cell surface proteins |
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| T Lymphocytes |
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| • 3 types: – Cytotoxic T cells – 2 types of helper T cells (TH1 & TH2) |
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| Cytotoxic T cells (TC Cells) |
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| • Distinguished by the CD8 cell-surface glycoprotein • Directly kill certain cells – Cells infected with viruses and other intracellular pathogens – Abnormal cells, such as cancer cells |
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| Helper T Cells (TH Cells) |
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| • Distinguished by the CD4 cell-surface glycoprotein • Function to “help” regulate the activities of B cells and cytotoxic T cells during an immune response • Secrete various soluble protein messengers, called cytokines, that determine which immune response will be activated |
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| Helper T Cells (TH Cells) |
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| • 2 types – Type 1 helper T cell (TH1): • Assist development of cytotoxic T cells and macrophage activation. – Type 2 helper T cell (TH2): • Assist development of B cells and antibody formation |
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| Effector T Cells Cytokines |
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| • Soluble regulatory proteins that act as intercellular signals when released from certain body cells • Immune system cytokines signal among various leukocytes • The complex web of signals among all the cell types of the immune system is referred to as the cytokine network |
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| Interleukins (ILs) |
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| signal among leukocytes |
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| Interferons (IFNs) |
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| antiviral proteins that may act as cytokines |
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| Growth factors |
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| proteins that stimulate stem cells to divide, maintaining a adequate supply of leukocytes |
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| Tumor necrosis factors (TNFs) |
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| Secreted by macrophages and T cells to kill tumor cells and regulate immune responses and inflammation |
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| Chemokines |
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| signal leukocytes to go to a site of inflammation or infection and stimulate other leukocytes |
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| Lymphocyte Editing by Clonal Deletion |
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| • Vital that immune responses not be directed against self (autoantigens) • Body “edits” lymphocytes to eliminate any self-reactive cells |
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| Major Histocompatibility Complex (MHC) |
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| • Group of antigens first identified in graft patients • Important in determining the compatibility of tissues in successful grafting • Major histocompatibility class I antigens are glycoproteins found in the membranes of most nucleated cells of vertebrate animals • Function to hold a peptide fragment from an intracellular protein (endogenous antigen) for presentation to T cells |
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| Major Histocompatibility Complex (MHC) |
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| • Antigens bind in the antigen-binding groove of MHC molecules • 2 classes of MHC proteins – MHC class I – MHC class II |
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| Number of Alleles in Caucasoids: Antigen Processing |
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| • T-independent antigen – Large antigen molecules with readily accessible, repeating antigenic determinants – B cells can bind and respond to these directly without T cell cytokine help • Stimulates B cells to differentiate into a plasma cell and produce antibodies |
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| Antigen Processing |
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| • T-dependent antigens – Smaller antigens with less accessible antigenic determinants – B cells require involvement from helper T cells to target these antigens – Helper T cells are assisted by antigen presenting cells that process the antigen and make the antigenic determinants accessible to T cells • Processing is different based on whether the antigen is exogenous or endogenous |
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| Processing of Exogenous Antigens |
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| • APC internalizes the invading pathogen and enzymatically digests it into smaller antigenic fragments which are contained within an endosome • Endosome fuses with a vesicle containing MHCII molecules • Each fragment binds to the antigen-binding groove of a complementary MHCII molecule • The fused vesicle then inserts the MHCII-antigen complex into the cytoplasmic membrane so the antigen is presented on the outside of the cell |
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| Processing of Endogenous Antigens |
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| • Intracellular proteins are broken down into smaller peptide fragments by the proteosome; fragments transported into endoplasmic reticulum (ER) • Each fragment binds to a MHCI molecule located in the ER • The membrane is packaged into a vesicle by a Golgi body which is inserted into the cytoplasmic membrane so the antigen is displayed on the cell’s surface |
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| Antigen Processing and Presentation Humoral Immune Response |
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| • Body mounts humoral immune responses against exogenous pathogens • Components of a humoral immune response – B cell activation and clonal selection – Antibody – Memory B cells and the establishment of immunological memory |
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| Plasma Cells |
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| • Make up the majority of cells produced during B cell proliferation • Each plasma cell secretes antibody molecules complementary to one specific antigenic determinant. • The class of antibody produced is determined by signals from T-helper cells • Are short-lived cells that produce massive amounts of antibody and then die within a few days |
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| Memory B Cells |
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| • Cells produced by B cell proliferation that do not secrete antibodies • Cells that have BCRs complementary to the specific antigenic determinant that triggered their production • Long-lived cells that divide only a few times and then persist in the lymphoid tissue • Are available to initiate antibody production more rapidly if the same antigen is encountered again |
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| Cell-Mediated Immune Response |
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| • Responds to intracellular pathogens and abnormal body cells • The most common intracellular pathogens are viruses but the response is also effective against intracellular bacteria • Triggered when antigenic determinants of the pathogen are displayed on the host cell’s surface |
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| Acquired Immunity |
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| • Specific immunity acquired during an individuals life • 2 types |
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| Naturally acquired |
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| immune response against antigens encountered in daily life |
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| Artificially acquired |
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| response to antigens introduced via medical intervention |
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| Active |
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| products made by the individual (humoral or cell-mediated responses) |
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| Passive |
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| passively receive antibodies made by another individual |
