The Immune System

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Innate Immunity

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Nonspecific defense mechanisms, including both extermal physical barriers of skin and mucous membranes and the internal defenses of chemicals and phagocytic cells

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Acquired Immunity

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aka adaptive immunity, line of defense in which lymphocytes react specifically to threat.

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Humoral defense

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antibodies produced by cells derived from B lymphocytes mark microbes for destruction.

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cell-mediated response

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cytotoxic lymphocytes destroy infected body cells, cancer cells, and foreign tissue

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Lysozyme

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an enzyme that attacks bacterial cell walls, is present in tears, saliva, and mucus.

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Neutrophils

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short-lived phagocytic white blood cells (leukocytes)

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Monocytes

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migrate into tissues and develop into macrophages, which are large, long-lived phagocytic cells. They may migrate through the body or become permanently attached in various organs, including the lymph nodes, spleen, and other tissues of the lymphatic system.

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Macrophages

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large, long-lived phagocytic cells. They may migrate through the body or become permanently attached in various organs of the lymphatic system.

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Eosinophils

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leukocytes that attack multicellular parasitic invaders with destructive enzymes.

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Dendritic cells

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their primary role is to stimulate acquired immunity and carry out phagocytosis.

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the complement system

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a group of about 30 serum proteins that, when activated, may lyse microbes, trigger inflammation, or assist in acquired defenses. Virus-infected cells produce two types of interferons that stimulate neighboring cells to produce substances that inhibit viral reproduction in those cells. Another type of interferon activates macrophages.

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interferons

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substances which are produced by virus-infected cells and stimulate neighboring cells to produce substances that inhibit viral reproduction in those cells. Another type of interferon activates macrophages.

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Inflammatory response.

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Chemicals released in response to physical injury or pathogen entry can trigger an inflammatory response, characterized by redness, swelling, and heat. Damaged mast cells in connective tissue release histamine, which triggers dilation and leakiness of blood vessels; activated macrophages and other cells release prostaglandins and other chemicals that promote blood flow to the damaged area.

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histamine

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produced by mast cells in connective tissue ... histamines trigger dilation and leakiness of blood vessels; activated macrophages and other cells relesase prostaglandins and other chemicals that promote blood flow to the damaged area.

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Chemokines

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Vasodilation as well as signaling proteins called chemokines result in the congregation of phagocytic cells and the production of antimicrobial compounds.

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natural killer cells

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recognize general features of virus-infected or cancer cells, attaching to them and triggering apoptosis, or programmed cell death.

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cytokines

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lymphocytes, the key cells of acquired immunity, are activated by contact with microbes and by cytokines, proteins secreted by macrophages and dendritic cells after they engulf microbes.

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Antigens

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foreign molecules recognized by lymphocytes. most are large proteins or polysaccharides, often protruding from the surfaces of microbes or transplanted cells.

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epitope

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antigenic determinant... The small region of an antigen to which a lymphocyte or secreted antibody binds is called an epitope.

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b lymphocytes and t lymphocytes

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aka b cells and t cells circulate in blood and lymph and reside in the spleen and lymph nodes

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antigen receptors

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both b and t cells have membrane bound antigen receptors that allow them to recognize specific epitopes

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b cell receptor

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y-shaped receptor consisting of four polypeptide chains: two identical light chains and two identical heavy chains, linked together by disulfide bridges. both heavy and light chains have variable regions at the ends of the two arms of the y, which form two identical antigen-binding sites. The constant regions vary little from cell to cell.

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immunoglobulins

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secreted antibodies, they lack anchoring transmembrane regions but are otherwise structurally similar to B cell receptors, which are often called membrane antibodies.

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T cell receptor

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anchored by a transmembrane region, consists of one alpha chain and one beta chain, linked by disulfide bridge. The variable regions at the tip of the molecule form a single antigen-binding site. T cells recognize small fragments of antigens complexed with MHC molecules

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Major Histocompatibility Complex (MHC)

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a family of genes which codes for cell-surface proteins. In a process of antigen presentation, newly formed MHC molecules bind with antigen fragments within the cell and then display them on the cell's surface, where a T cell receptor can recognize the antigen and MHC molecule complex.

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Class I MHC molecules

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are found on almost all nucleated cells. They bind foreign antigens that an infected of cancerous cell has produced. Cytotoxic T cells recognize class I MHC molecules displaying peptide antigens.

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Cytotoxid T cells

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recognize class I MHC molecules displaying peptide antigens.

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Class II MHC molecules

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made by dendritic cells, macrophages, and B cells. These cells, called antigen-presenting cells, engulf and fragment microbes and display their antigens in class II MHC molecules.

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Antigen-presenting cells

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engulf and fragment microbes and display their antigens in class II MHC molecules.

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Helper T cells.

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recognize class II MHC molecule-peptide antigen complexes.

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thymus

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lymphocytes either migrate to the thymus and differentiate into T cells or continue to develop in the bone marrow as B cells

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effector cells

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short-lived cells which combat the antigen

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memory cells

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long-lived cells which carry receptors for a particular antigen

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clonal selection

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a small number of cells is selected by their interaction with a specific antigen to produce thousands of cells keyed to that particular antigen.

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primary immune response

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the body mounts a primary immune response upon first exposure to an antigen.

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plasma cells

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antibody-producing effector B cells

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secondary immune response

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more rapid, effective, and prolonged than primary immune response. The long-lived T and B memory cells are responsible for immunological memory

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humoral immune response

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involves B cell activation and production of antibodoes that circulate in the blood and lymph and defend against pathogens and toxins in estracellular fluid

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cell-mediated immune response

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involves cytotoxic T cells that destroy infected body cells, cancer cells, and transplanted tissues. Helper T cells activate both B cells and cytotoxic T cells

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CD4

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A T cell surface protein which enhances the binding between an antigen-presenting cell and helper T cell, which results in the proliferation and differentiation of a clone of activated helper T cells and memory cells.

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Activated helper T cells secrete cytokines, which stimulate __________________

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the cell-mediated and humoral responses.

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Helper T cells recognize ______________ complexes on antigen-presenting cells

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Helper T cells recognize specific class II MHC molecule-antigen complexes on antigen-presenting cells.

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CD8

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surface proteins on cytotoxic T cells bind to the side of class I MHC molecules and enhance the interaction between the cells, while the cytotoxic T cells, also stimulated by cytokines from nearby helper T cells, differentiate into active killers.

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monoclonal antibodies

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a technique for making monoclonal antibodies can supply quantities of identical antibodies

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membrane attack complex

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antigen-antibody complexes on microbes or transplanted body cells may activate the complement system by binding with complement system by binding with complement proteins and triggering the generation of a membrane attack complex *MAC*, which produces a pore in the membrane and causes the cell to lyse.

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Active immunity

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can be acquired when the body produces antibodies and develops immunological memory from either exposure to an infectious agent or from immunization aka vaccination

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passive immunity

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temporary immunity is provided by antibodies supplied through the placenta to a fetus, through milk to a nursing infant, or by an antibody injection.

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Rh factor

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a protein red blood cell antigen, if fetal blood from an Rh positive child leaks across the placenta. Should she carry a second Rh positive fetus, her immunological memory may result in the production of IgG antibodies that cross the placenta and destroy fetal red blood cells.

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graft versus host reaction

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the lymphocytes in the bone marrow transplant may produce a graft versus host reaction if the MHC molecules of donor and recipient are not well matched

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anaphylactic shock

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a severe allergic response in which the abrupt dilation of peripheral blood vessels caused by widespread mast cell degranulatoin leads to a life-threatening drop in blood pressure

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acquired immunodeficiency syndrome AIDS

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suppresses the immune system

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HIV

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infectious agent responsible for AIDS... HIV infects cells with surface CD4 molecules, including helper T cells, macrophages, and brain cells. CD4 and a protein co-receptor, which normally functions in chemokine reception, are required for viral entry. HIV RNA is reverse transcribed into DNA, which is integrated into the host cell genome, from where it directs production of new viral particles.