The role of the immune system is to provide a defense mechanism against foreign cells, including infectious organisms: Macrophages are phagocytic cells located throughout the body that play an important role in killing pathogens B-cells (a subset of leukocytes) prevent bacterial infection T-cells (lymphocytes) also play an integral role in the immune system.
The innate immune system is the first-line defense against pathogens, mediated primarily by the phagocytic monocyte, macrophage, and polynuclear neutrophils. These cells bind to a variety of microbial products using a basic recognition system and then internalize and destroy pathogens with powerful enzymes. The reaction of the immune system can be broadly categorized as either innate or adaptive responses. Once a pathogen gains entry into the body through the skin or another host barrier, macrophages and other phagocytic cells respond rapidly to defend the body against the invasion. NOTE: Macrophage needs to display the antigen. Medical illustrator is modifying the graphic.
The reaction of the immune system can be broadly categorized as either innate or adaptive responses. Once a microorganism gains entry into the body, macrophages and other phagocytic cells respond rapidly to defend the body against invasion. An immune response to a foreign antigen requires the presence of a macrophage which is an antigen-presenting cell (APC). When an APC presents an antigen on its cell surface, the B-cell is signaled to proliferate and produce antibodies that specifically bind to that antigen If antibodies bind to antigens on bacteria, it acts as a signal for macrophages to phagocytose and kill them When antibodies bind to cells or bacteria, serum proteins called complement, which induce antibody-coated cell lysing, bind to the immobilized antibodies and destroy the bacteria in a rapid response to a microbial invasion Antibodies can signal NK cells and macrophages to kill viral or bacterial-infected cells, and can activate complement.
Vip immunity to infections
<ul><li>Immunity to infections </li></ul><ul><li>Prof M.I.N. Matee </li></ul>
About this Chapter <ul><li>Anatomy & function of immune system, organs, & cells </li></ul><ul><li>How the body defends itself </li></ul><ul><li>Non-specific body defenses </li></ul><ul><li>Specific defenses that target one pathogen </li></ul><ul><li>Combined defenses against bacteria and viruses </li></ul><ul><li>Allergies and autoimmune problems </li></ul>
Immune System Functions: Overview of Defenses <ul><li>Scavenge dead, dying or abnormal (cancerous) body cells </li></ul><ul><li>Protect from pathogens & foreign molecules </li></ul><ul><ul><li>Parasites </li></ul></ul><ul><ul><li>Bacteria </li></ul></ul><ul><ul><li>Viruses </li></ul></ul>
Immune System Functions: Overview of Defenses Figure 24-1: Viruses
<ul><li>Activate T lymphocytes: direct attack </li></ul><ul><li>Activate B lymphocytes to become: </li></ul><ul><ul><li>Memory cells: 2 0 immune response to that antigen </li></ul></ul><ul><ul><li>Plasma cells: antibodies – attack that antigen </li></ul></ul>Acquired Immunity: Antigen-Specific Responses
Acquired Immunity: Antigen-Specific Responses Figure 24-13: Functions of antibodies
<ul><li>T cell receptors: cell activated to antigen </li></ul><ul><li>Major histocompatability complex (MHC) </li></ul><ul><li>Helper T cells: </li></ul><ul><ul><li>Cytotoxic T cells: perforins, granzymes, (apoptosis) & Fas </li></ul></ul>T Lymphocytes: Cell Mediated Immunity
T Lymphocytes: Cell Mediated Immunity Figure 24-16: T lymphocytes and NK cells
<ul><li>Make membrane attack complex kill bacteria </li></ul><ul><ul><li>Inflammation: + recruit phagocytes, B & T lymphocytes </li></ul></ul><ul><ul><li>(Acquired response antibodies, cytotoxic Ts … if needed) </li></ul></ul>Defenses against Bacteria: Complement P Activates:
Defenses against Bacteria: Complement P Activates Figure 24-17: Immune responses to bacteria
<ul><li>Circulating antibodies inactivate or target virus (opsins) </li></ul><ul><li>Macrophage inflammation, interferon, cell activation </li></ul><ul><ul><li>Helper, cytotoxic T, NK & B cells plasma c. antibodies </li></ul></ul>Viral Defense: Summary of Innate & Acquired Responses
Viral Defense: Summary of Innate & Acquired Responses Figure 24-18: Immune responses to viruses
Summary <ul><li>Body defends itself with barriers, chemicals & immune responses </li></ul><ul><li>WBCs and relatives conduct direct cellular attack: phagocytosis, activated NK & cytotoxic T cells and produce attack proteins (i.e. antibodies, complement, & membrane attack complex) </li></ul>
Summary <ul><li>Cytokines, communicate cell activation, recruitment, swelling, pain, & fever in the inflammation response </li></ul><ul><li>Defense against bacteria is mostly innate while viral defense relies more on acquired immune responses </li></ul><ul><li>Autoimmune diseases are a failure of self-tolerance </li></ul>
Viruses NNatural Immunity Virus infection directly induce the production of IFN, which inhibit viral replication and the expression of MHC molecules NK cells lyse virally infected cells. IFN enhance the activity of NK. TThus NK is the primary natural immune response to viral infection. Acquired Immunity Ab are important during early viral infection. Ab prevents entry to the host cells and opsonize viral particle for phagocytosis. CTL is important for established infection. Both CD4 and CD8 CTLs participate.
Immunity to Extracellular Bacteria Live in tissue space and induce inflammation and tissue destruction Release toxins: Endotoxin: bacteria cell wall components Exotoxin: secreted by bacteria. Toxins induce cell activation and modulate activities of kinases and other enzymes. Immunity to extracellular bacteria is aimed to eliminate the bacteria and neutralizing toxins. Natural Immunity: Phagocytes Complement via the alternative pathway: C3b opsonize bacteria, C9 lyse bacteria and other by-products promote inflammation. Toxins could lead to the production of cytokins. Uncontrolled cytokine production could result in septic shock. Example: LPS activate macrophages to produce TNF Adoptive Immunity Humoral immunity is the principal protective mechanism IgG opsonize bacteria by binding to FcR on phagocytes. IgG and IgM neutralizing bacteria and prevent binding to cells Activate the complement system. C3b promotes phocytosis activity. CD4 T cells help antibody production and produce cytokines to help phagocytosis. Some Toxin can be superantigens.
Intracellular Bacteria Natural Immunity Can survive with in phagocytes due to the ability to interfere with lysosome movement. Natural immunity are quite ineffective. Difficult to eradicate and could cause chronic infections NK cells are the main force against intracellular infection. Acquired Immunity Mainly CMI. Type I CD4 cells activated by released antigens will produce IFNgamma which activate macrophages (RO) to effectively kill. CD4 cells also help CD8 cells to kill. Activated macrophages during DTH cause tissue injury. Chronic antigen stimulation leading to granulomas, the histological hallmark. Granulomas limit spread but also cause tissue function impairment.
PParasites Parasites often have many stages. Some of the stage are in intermediate hosts. Natural Immunity Not effective Whenever enter tissue or blood, parasite could survive and replicate. Complements are ineffective. Phagocytes could be replication factory. Acquires Immunity Diverse response to various parasites IgE and eosonophil are important for helminth infections. Driven by IL-4 and IL5. Eosinophil granules are toxic to helminthes. Granuloma formation to contain parasites and eggs. Intracellular parasite stimulate CTL.