Protective immunity to microbes

Protective immunity to microbes - ‫بسم اللة...

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Unformatted text preview: ‫بسم اللة الرحمن‬ ‫الرحيم‬ Protective Immunity Protective Immunity To Microorganisms Protective Immunity To Microorganisms Protective Defense against microbes is mediated by: Innate immunity and acquired immunity Humoral immunity (antibodies) Through both Cell mediated immunity (CMI) Antibacterial Immunity Antibacterial I) Immunity to extracellular bacteria: 1­ The innate immunity: a­ Complement activation b­ Phagocytosis c­ The inflammatory response I) Immunity To Extracellular Bacteria I) 2­ The acquired immune responses: i­The humoral mechanisms (antibodies) “main role” ii­ Cell mediated immune response “less role” i­ Antibodies induce immunity through: a­ Neutralization of bacterial toxins b­ Antibodies attach to the surface of bacteria and; ­ Act as opsonins, enhance phagocytosis (Opsonization) ­ Prevent adherence of bacteria to their target cells e.g. IgA on mucosal surfaces ­ Activation the complement leading to bacterial lysis ­ Agglutinate bacteria, preventing their spread and facilitating phagocytosis I) Immunity To Extracellular Bacteria I) ii­ Cell mediated immune mechanisms: * Microbes are internalized by APCs and presented to TH * TH cells are activated and release cytokines which; ­ activate phagocytosis their microbicidal functions ­ Stimulate antibody production ­ Induce local inflammation Immunity To Intracellular Bacteria Immunity 1) Innate immunity It is mainly by natural killer (NK) cells ­ They kill infected cells and secrete IFN­γ ­ IFN­γ activate phagocytosis to kill intracellular microbe E.g. tuberculosis, leprosy, listeriosos 2) Acquired immunity is manly by CMI ­ Activation of macrophages to kill intracellular microbes ­ Lysis of infected cells by cytotoxic cells (CTLs) ­ Most of these organisms are resistant to phagocytosis, cause chronic infection and granuloma formation Anti-Viral Immunity Anti-Viral 1) Humoral immunity: a­ Virus neutralization * In viraemic infections, Antibodies neutralize virus, preventing its attachment to receptor sites on susceptible cells e.g. Poliovirus, mumps, measles, rubella * In superficial non­viraemic infections (infleunza) Secretory IgA neutralizes virus infectivity at the mucous surfaces Anti-Viral Immunity Anti-Viral 1) Humoral immunity: b­ Antibodies destroy free virus particles directly by: i­ Aggregation of virus and opsonization ii­ Complement mediated lysis * Both mechanisms also act on virus infected cells Anti-Viral Immunity Anti-Viral 2) Cell mediated immunity: Cell mediated cytotoxicity, mediated by : ­ Cytotoxic T­cells (CTLs) ­ NK cells ­ Activated macrophages Anti-Viral Immunity Anti-Viral CMI acts on virus infected cells through: ­ CTLs kill virus infected cells directly after recognition of viral antigens on cell surface in association with MHC I ­ TH­cells stimulated by viral antigens release cytokines Cytokines attract and activate macrophages to kill virus infected cells ­ Nk­cells destroy virus infected cells early in infection before appearance of antibodies ­ Antibody­dependent cell mediated cytotoxicity (ADCC): Antibody binds to virus infected cells such cells are lysed by NK cells, macrophages and polymorphs Anti-Viral Immunity Anti-Viral 3) Anti­viral activity of interferons (IFNs) 1­ Virus infected cells produce INF­α; ­ INF­α inhibit intracellular replication of viruses ­ IFN­α activate NK­cells to kill virus infected cells ­ IFNs have no direct effect on extracellular virus ­ IFNs act early in viral diseases before antibody ­ INFs activity is not specific Anti-Fungal Immunity Anti-Fungal Immune response to fungi consist mainly of : 1) Innate immunity is mediated by: ­ Neutrophils and macrophages ­ Fungi are readily eliminated by phagocytes 2) Acquired immunity (cell mediated immunity) ­ CMI acts in a manner similar to its action against intracellular bacteria * Disseminated fungal infection are seen in: immunodifcient persons Thanks Thanks ...
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